crankshaft bolt - put the ratchet on it from below, hold it! and get someone to turn the ignition key just so it cracks the bolt, little tip to get that off
MARK the cam and crank pulley before you take them off.
replace timing belt, water pump/gasket/tensioner if it's worn, threadlock the bolts! tension the timing belt, it should twist 90 degrees, and if you pull it it should have a nice whip on the belt (you'll see what i mean) turn the engine over via the crank bolt (a few turns of the pulley) to makesure nothing is making contact!
oh and refill with uncle freeze