This is a belated response to a NAG writing challenge.
I don't know how many times I have saw the mistaken use of the words effect and affect while doing reviews. The best way to remember the difference is to ask oneself how one wants to use the words. If one wants to use it as a verb and thus an action word then it would be spelled "affect". If however one wants to use it as a noun the proper spelling is "effect".
Here are some samples of the words used in a story.
The psychiatrist was concerned about the patient's behavior. The patient was exhibiting no emotions.. In psychological terms this is called flattened affect.
The doctor started the patient on an antidepressant but had to discontinue the medication because it had a negative side effect.
In both of the examples above I have modified the subject words with adjectives for clarification.