Well, you want to be sure that you had put stabilizer in your gas before you put your sled away last spring. If you didn't......siphon the gas out, and get rid of it.
Pull all the carbs apart, and clean them thouroughly. Pull and clean
ALL the jets. Make sure the air and idle screws are synced and in spec.
Change your oil and gas filters.
Grease all front and rear suspension components with low temp grease.
Grease jack and drive shafts on the pto side.
Grease any steering components that you have access to.
Adjust the throttle and choke cables if they need it.
New belt and spark plugs........make sure you have spares for each as well.
If your coolant hasn't been changed in a couple of years, you might want to do that. At least make sure its topped off.
The same goes for your gear case oil. If it hasn't been change in a while, you might want to change that as well. Again, make sure its up to the correct level.
Check the fluid level in your battery and give it a good charge (if you've got one).
Check your track tension, and adjust if its out of spec.
Check your ski alignment, and adjust if its out of spec.
Check your wear rods, and replace if their shot.
Look for any and all loose bolts, in the engine compartment and especially rear suspension.
If your clutches haven't been looked at in a while, you might want to consider having them rebuilt. But if they were operating well last season, then they're probably still ok.
I guess thats all I can think of right now. Good luck.
1997 XLT SP 600
"Engage the Mechanism"