before you attempt to start it check the oil if its clean and at the right level turn the engine over by hand a few times to lubricate the innards as the oil may well have drained off the cylinder walls.
check your other fluid levels too.
did you give the battery a full charge, ideally a trickle charge overnight and then check it to see if it's holding the charge. sometimes an unused battery can oxidise on the plates through lack of use and when you charge it it wont hold a charge.
ensure the terminals and earth straps are clean from corrosion and secure.