Over the course of many years, people have used the words "Belief" and "Faith" interchangeably, and without seeming to notice the subtle differences between them. So I've compiled a few personal definitions that I go by when conversing or corresponding with someone on matters of belief and faith. Here they are:
Belief: An opinion, especially one that may be easily changed or discarded.
Simple Belief: A personal conclusion or opinion held to be valid, regardless of whether or not it has any inherent validity.
Firm Belief: (1) Belief based on verifiable data or demonstrable principles; (2) Belief that is based upon experiment, reason, and research.
Faith: A strongly-held opinion, especially one that is unlikely to be changed or discarded.
Simple Faith: (1) Belief without supporting data or principles; (2) Belief that is based upon emotional sensations, subjective feelings, or intuitive impressions; (3) Belief that is based upon written apocrypha, legend, or myth; (4) Belief that is based upon verbal anecdote, hearsay, or rumor.
Blind Faith: (1) Belief without true understanding, perception, or discernment of what is believed; (2) Belief that exists in contradiction to valid data and demonstrable principles; (3) Belief that exploits the gullibility or ignorance of the believer for the amusement or personal gain of others.
The following maxims are useful to this topic:
"Entities must not be multiplied beyond necessity." This means that the simplest cause or group of causes for an event are all that is necessary for that event to occur. There is no need to propose an improvable cause or a subjunctive ("what if...") condition to explain an event. This is called the "Principle of Parsimony" or "Occam's Razor".
"Extraordinary claims require extraordinary proof, and the burden of proving the claim is upon the claimant." This means that when a claim is made that requires a violation of a known natural principle (or reasonable extrapolation thereof), the claimant is the person that must prove the validity of that claim.
"If the absence of a thing is indistinguishable from it's alleged presence, then it is reasonable to claim that the thing does not exist." If a man claims to own a yacht, live in a mansion, and drive a Ferrari, yet he is never seen with any of those things, it is safe to assume that none of his claims are true, and that there is no yacht, mansion or Ferrari.
"It is enough to admit that a thing is aesthetically pleasing without claiming a supernatural cause for its beauty." Just because a person may feel a sense of euphoria inspired by the presence of beauty, it does not mean that the feeling has a supernatural cause.
"Physical events require only physical causes." This correlates well with the previous maxim.
"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sir Arthur Conan Doyle made this the operative principle of his most famous literary creation -- Sherlock Holmes.
Familiarity with the common fallacies of logic is also useful. Here is a link to a very useful List of Common Fallacies of logic.
And one of the most common errors that an individual may make is to rely solely upon his or her own reasoning, without going to the trouble of verifying his or her opinions, and thus accepting those opinions as unshakable facts and universal truths. This is also known as "Solipsism".