To start, here are some of the things you should do to maintain your dirt bike:
 
Give your dirt bike a general dirt bike check-up regularly by checking for loose bolts and spokes, to make sure that everything is where it should be.

Whenever you want to take your dirt bike for a spin, much more when you need to compete in a race, always check your chain tension and lube it when necessary. Also ensure that your air filter is clean. When required, clean or change it right away.

You should also check and maintain your dirt bike parts between outings.  Wash your dirt bike and get rid of the dirt and grime from your last outing. Also, make sure that your brake pads are still ok. Take note of your controls for smooth operation and inspect cables for fraying.

When checking your dirt bike, test your chain and sprockets for wear. These dirt bike parts experience most of the abuse when you race. Verify your gearbox oil level, as well as your engine oil level if you ride a four stroke. Ensure that your radiators are free of damage and leaks. In addition, check your coolant level. 

All in all, providing your dirt bike with the proper care it needs will ensure safer and more secure rides.