Yeh, basically what Unit MX said but im not at strict with my maintenance...
Most people don't keep pitties (apart from genuine thumpstars etc.) much longer than a year or 2...
Basically...
Change you're oil when you can see it's getting dark, usually after a few rides but depends whether you ride at tracks or not...
Buy Uni Filter and clean it regulary...
New spark plug every now and then
Tighten all the bolts
Clean the carby
Replace the piston rings if you start burning oil (blue smoke and lower compression than usual)
I'm not sure how often you replace your piston but not very often, unless you race.
Replace brake fluid
Replace brake pads every so often...
Also you need to loctite ALL the bolts, ESPECIALLY the bolts on the muffler/exhaust as they rettle like crazy..(mine came loose with loctite!)
If you do anough maintenance, these bikes are a lot of fun and they will last quite long...