Opinions will very pretty widely, but other than the basic maintenance that comes with any MX bike (chain adjustment, clean air filters, etc) a few things are absolute with a high-rpm four-stroke like this.
- change the oil and filter every couple of hard rides
- check the valve clearance every 5-10 hours, when the clearance starts moving it's usually a sign that it's time to open it up and inspect the valves, springs and seats
- clean the carb vents every couple of rides
- put an hour meter on the bike and use it along with the factory service intervals to help determine crank and rod life
The factory manual has a very good service interval chart that is worth the time to get familiar with.