[Overpaid Slacker]

it's is essentially the contraction for "it is". The sneaky part is that we're used to using an apostrophe for a possessive, where the possessive "its" does not have one. If you could write "it is" instead of whatever permutation if i t and s you're going to use, then it's "it's".

Affect = Verb -- I'd remember it like A is an upside-down V (for verb)
Effect = Noun -- Try "Side effect" -- obviously a noun, to remember that "effect" is the noun.

next week: rules for semi-colons.

JP