I seem to have a problem distinguishing the times to use one or the other. The general rule is that good is an adjective and well is an adverb. This means that good modifies nouns, and well modifies verbs, adjectives and other adverbs. The general rule, however, has dozens of exceptions, and many of these are found in very common English constructions. For example, well can be used as an adjective meaning suitable, proper, or healthy .
Some grammarians claim that such exceptions are largely colloquial.
If this is the case, they have been colloquial for hundreds of years. Surely by now they have some claim to be labeled as common usage. I ll do good on your final exam. I ll do well on your final exam. No one who asks this question is likely to do well on my final exam.