You should do a search but since im posting anyway you could try a bigger rear sprocket, flywheel weight, FMF Fatty pipe, and I find using a good tire meant for the conditions you ride in to work wonders.
Start by adding some protection on the bike with like handguards and a skid plate. Then set the suspension up for the type of traisl you ride, and finally look for aftermarket parts that will help you with some more bottomend such as cylinder porting, reed vavle, different gearing, flywheel weight, pipe/silencer, and jet it!