Affect is less commonly used to refer to mood, strangely enough..
"disorders of affect" can affect women more than men ;-)
I'd say "affect" is to have an influence or impact upon and is a verb : something you do.
"Effect" is an outcome or result of something (and often a noun). Even in saying "What effect will this drug have" you're referring to what outcome/end product.
To "effect" change, to bring about or result in change would be to use it as a verb but this isn't as common