+ who gets diluted
+ vesting schedule
+ does vesting accelerate with an acquisition?
+ liquidation preferences
+ how large is the employee option pool
+ what happens to your holding on a down-round or restructure (this is hard not to get screwed on if this is the intention)
+ not checking that the options agreement has been signed by the company
+ not signing an options agreement and taking the company and/or founder at their word that you have stock
founders usually give themselves a sweet deal. ask to see their agreement and compare it to yours.
while you are at it, check the structure of the board and if the board are able to block an acquisition. you may be working for a company who can't exit unless the investors get at least 4-5x, and if they don't, you get nothing
there are probably some things that I am missing, which is why it is worth paying a lawyer for 3-4 hours of time to go over it (not the company lawyer - see 'the social network')