aggie I have to stop and think with its and it's, so if I am in a hurry I try to avoid them both.
The logic behind them is that it's is a shortened form of it is (like I'm and he's and we're and they're) and its is possession, but it doesn't need the apostrophe because it already has the possessiveness built-in (like my, his, her, our, your, their)
If in your mind you can bracket it's with I'm and he's, and bracket its with my and your, it may be easier. (but it's yet another thing to remember when you are busy typing!)
The other punctuation that catches me out is the colon : and the semicolon : so I avoid them too, if I can.