An article by Prof. Frank Wolfs at University of Rochester with a rather well written and clear description of what science is.......
http://www.answersinscience.org/FrankWolfs.html

An article on the Talk.Origins site with a brief explanation of the concept of science and scientific evidence......
http://www.talkorigins.org/faqs/comdesc/sciproof.html

Creationists confuse and misuse (and often deliberately) the terms ontological (philosophical) naturalism and methodological naturalism. The former is the view that nothing supernatural exists - a point which may engender heated debate among theologians and philosophers but is irrelevant to the pursuit of science....... http://www.answersinscience.org/MethodologicalNaturalism.htm

The PBS website containing a multitude of resources to help answer this question........ http://www.pbs.org/wgbh/evolution/library/09/index.html

One of the more concise definitions of science I have seen was that given by Edward O. Wilson and published in the American Scientist,  Jan/Feb 1998, pg.6.

"Science, ... is the organized systematic enterprise that gathers knowledge about the world and condenses the knowledge into testable laws and principles. The diagnostic features of science that distinguish it from pseudoscience are first, repeatability: The same phenomenon is sought again, preferably by independent investigation, and the interpretation given to it is confirmed or discarded by means of novel analysis and experimentation. Second, economy: Scientists attempt to abstract the information into the form that is both simplest and aesthetically most pleasing the combination called elegance while yielding the largest amount of information with the least amount of effort. Third, mensuration: If some thing can be properly measured, using universally accepted scales, generalizations about it are rendered unambiguous. Fourth, heuristics: The best science stimulates further discovery, often in unpredictable new directions; and the new knowledge provides an additional test of the original principles that led to its discovery. Fifth and finally, consilience: The explanations of different phenomena most likely to survive are those that can be connected and proved consistent with one another.

Science can be defined in a number of ways.

Webster's Dictionary defines science as "the observation, identification, description, experimental investigation, and theoretical explanation of natural phenomena."

The Oxford English Dictionary defines science as "a branch of study which is concerned with a body of demonstrated truths or observed facts, systematically classified and more or less colligated by being brought under general laws, and which includes trustworthy methods for the discovery of new truths within its own domain."

Cuffey adds that "using actual practice as the basis for definition, we can define 'science' simply as the attempt to understand natural phenomena more completely by means of repeatable or verifiable observation. (This is broader than the rigid, prediction or experiment-oriented definitions developed by some philosophers not actively engaged in scientific work.)" (Montagu, pg. 269).

"Science is devoted to formulating and testing naturalistic explanations for natural phenomena. It is a process for systematically collecting and recording data about the physical world, then categorizing and studying the collected data in an effort to infer the principles of nature that best explain the observed phenomena."

It is guided by natural law. 
It has to be explanatory by reference to natural law. 
It is testable against the empirical world. 
Its conclusions are tentative (are not necessarily the final word). 
It is falsifiable (Ruse, from Montagu, pg. 340)

Ask a question about some discrete part of the natural world. 
Research the question to determine how much is already known about it. 
Propose a solution to the question (HYPOTHESIS) which may explain it. A hypothesis is an imaginative preconception of what might be true in the form of a declaration with verifiable deductive consequences (Futuyma, pg. 167). 
Devise a controlled experiment which will either support or refute the hypothesis. 
Conclude based upon the facts derived by the experiment and existing scientific theories whether the hypothesis should stand, fall, or be revised. 
After surviving many tests a hypothesis may be elevated to the level of a THEORY.

observation, 
statement of the problem, 
formulation of hypothesis and predictions - induction,
experimentation, 
collection and interpretation of data, 
error analysis, 
stating of conclusions - often based on deductive reasoning.

Observation - gathering data through the senses or sensory enhancing technologies 

The collection of facts "The grist for the mill of scientific inquiry is an ever increasing body of observations that give information about underlying 'facts.' Facts are the properties of natural phenomena, The scientific method involves the rigorous methodical testing of principles that might present a naturalistic explanation for those facts.

Problem stating - 
Notation of discrepancies helps to form a basis for the statement of problems.

Hypothesis and prediction - Inductive reasoning 
Based on well established facts, testable hypotheses are formed. The process of testing "leads scientists to accord a special dignity to those hypotheses that accumulate substantial observational or experimental support." This "special dignity" is denoted by the granting of the title "theory," which, when it "explains a large and diverse body of facts" is considered "robust" and if it "consistently predicts new phenomena that are subsequently observed," it is "reliable."

Experimentation - 
is "A test under controlled conditions that is made to demonstrate a known truth, examine the validity of a hypothesis, or determine the efficacy of something previously untried."
The American Heritage Dictionary of the English Language, Third Edition
Testing hypotheses generated by historical sciences (where direct experimentation is impossible) requires the scientist to patiently wait for "new" data to be uncovered from the historical source.
"If you're doing an experiment, you should report everything that you think might make it invalid - not only what you think is right about it: other causes that could possibly explain you results." Feynman, 1988 p 247.

Conclusion - 
A deduction; making specific predictions from the general conclusions. As part of a conclusion the researcher will suggest a means of verification, that is checking the predictions against further observations. This allows the scientific method to be self-correcting.

putting forward a hypothesis 
conjoining it with a statement of 'initial conditions' 
deducing from the two a prediction, and 
finding whether or not the prediction is fulfilled" (Bynum, Browne, Porter, 1981, p. 196.

A discussion at "The methodology of scientific research programs" will give you a better idea of what science is and how to tell it from pseudoscience.

According to S. J. Gould "in the American vernacular, 'theory' often means 'imperfect fact' - part of a hierarchy of confidence running downhill from fact - theory - hypothesis - guess". But Gould points out that "facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world's data. Theories are structures of ideas."

Isaac Asimov states that "a theory is a detailed description based on long observation and, where possible, experiment. It is the result of careful reasoning from these observations and has survived the critical study of scientists generally." For more about Scientific Theories go to Asimov's Relativity of Wrong.

G.G. Simpson reminds us that "a fact is something that can be observed and that can be confirmed by the observations of others. ...Truth is interpretation of fact, and part of the scientific attitude is that any such interpretation is subject to correction. Truth in this sense can only be relative or tentative".

Although the scientific method has been established and dutifully followed, does it improve critical thinking and discovery?  Physicist Robert March maintains that the scientific method only applies to the way facts and ideas are tested. Discovery however follows a different pattern more often than not, "a lucky guess based on shaky arguments and absurd ad hoc assumptions gives a formula that turns out to be right, though at first no one can see why on earth it should be."

K. C. Cole points out that "Ideas like Einstein's relativity, Bohr's atom, and Copernicus's sun-centered solar system went against most current facts - not to mention most common sense." "Discovery consists of seeing what everybody has seen and thinking what nobody has thought." (A. Szent-Georgi)

Thomas Kuhn (MIT science historian) postulates that the scientific method is "a strenuous and devoted attempt to force nature into the conceptual boxes supplied by professional education." However this is not a bad thing since without some means of focusing in on the enormous quantity of information, scientists could never "penetrate existing knowledge to the core."

This must always be tempered with the understanding that "the scientist believes in proof without certainty, the bigot in certainty without proof. "Let us never forget that tyranny most often springs from a fanatical faith in the absoluteness of one's beliefs." (Ashley Montagu, pg. 9) 

Curiosity 
Veracity (excommunication for telling lies or falsifying data.) 
Testing hypothesis of the world against the external world by using one or all of the following:

Experiment 
Observation and recording followed by analysis 
Comparative studies of systems which are alike in some respects but different in others. 
Abstention form threat

"Science does not claim to have all the answers. Science is a way of looking at things, and the first approach of a scientist is to doubt and not believe." (Halstead)

In order to determine if science and its theories are justifiable, and provide the best possible explanation of the natural world, the theory must pass numerous tests. In other words it must be repeatable.

Once a theory is established it will exert a powerful influence over further scientific investigation. "Successful theories establish themselves as the 'paradigm' for scientific activity: They define not only acceptable techniques for tackling problems but also which problems to be considered relevant subjects for scientific investigation" (Bowler, pg. 15)

"On principle, it is quite wrong to try founding a theory on observable magnitudes alone. It is the theory which decides what we can observe." (A. Einstein, from J. Bernstein, "The Secret of the Old Ones, II." New Yorker, March 17, 1973).

Science historians and philosophers have established four areas for theory evaluation. These include logical, empirical, sociological, and historical criteria.
(The above From Robert Root-Bernstein in Montagu, pg. 64-94).

Logical Criteria
Simple unifying idea that postulates nothing unnecessary - Occam's razor. 


Logically consistent internally. Premises must hold true under conditions of the real world. 
Logically falsifiable - cases must exist in which the theory could be imagined to be invalid. Otherwise tautologies (circular reasoning) or there logically sterile constructions might be admissible as theories. 
Clearly limited by explicitly stated boundary conditions so that it is clear whether or not any particular data are or are not relevant to the verification or falsification of the theory. An unbounded theory is not falsifiable. And if a theory can not be falsified it cannot be self corrected. Yet self correctability is exactly the characteristics that gives a theory its epistemological power.

Empirical criteria (derived from observation or experiment)
The theory must be empirically testable itself or lead to predictions or retrodictions that are testable. A retrodiction predicts what has happened in the past. 


The theory should actually make verified predictions and/or retrodictions which are reproducible. 
The theory should provide criteria for the interpretation of data as facts, artifacts, anomalies or as irrelevant.

Sociological criteria
The theory should resolve recognized problems, paradoxes, and/or anomalies irresolvable on the basis of preexisting theories, and must be of the domain of science. 


The theory should pose a new set of scientific problems upon which scientists may work. 
The Theory must posit a "paradigm" or problem solving model by which these new problems may be expected to be resolved. It should be stated in terms that are operationally useful. 
It should provide definitions of concepts or operations beneficial to the problem-solving abilities of other scientists.

Historical criteria
The theory must meet or surpass all of the criteria set by its predecessors or demonstrate that any abandoned criteria are artifactual. 


The theory should be able to accrue epistemological status acquired by previous theories through their history of testing. 
Finally the theory should be consistent with all preexisting ancillary theories that already have established scientific validity. Without such criteria scientists would be able to pick and choose data that favor their previously recorded evidence and ignore theories that falsify their own ideas.

 
Eldredge, Niles. 1982. The Monkey Business (A Scientist Looks at Creationism). Washington Square Press.

Futuyma, Douglas J. 1982. Science on Trial (The Case of Evolution.) Pantheon Books, New York.

Kitcher, Philip. 1984. Abusing Science (The Case Against Creationism.) MIT Press.

McGowan, Chris. 1984. In the Beginning (A Scientist Shows Why the Creationists Are Wrong). Prometheus Books.

Montagu, Ashely, Ed. 1984. Science and Creationism, Oxford University Press.

Ruse, Michael. 1982. Darwinism Defended (A Guide to the Evolution Controversies). The Benjamin/Cummings Publishing Co.