Well, for a 21 year old bike, this is what I'd do for starters...
1) Change the oil. I like Mobil 1 15-50 synthetic (red cap).
2) Clean the air filter.
3) Disassemble and clean the carburetor with carb cleaner. Probably some gummy, varnished spots that need to be cleaned.
4) Drain and flush the gas tank. Put in fresh gas.
5) Ensure you have the correct spark plug, and that the gap is set correctly. I'd put a new one in. Make sure you have spark.
6) Ensure that the throttle tube and cable assembly is well lubed.
7) Start it up!
8) Take a little ride in the snow for a big grin!