I have owned many pit bikes some worth $300 and have managed to make them last for a few years by generally looking after them. This includes applying loctite to bolts and making sure everythings tight each ride. Straight away you should be dumping the oil and brake fluid that you get with your pit bike and replacing it with good quality oil/fluid. After that the engine oil should be changed approximately after every 7 hours of riding.
If you don't want parts constantly breaking on your bike be sure to purchase a new set of brake & clutch levers, a new air filter and any other parts that are constantly being used. It is also a good idea to upgrade your handlebars to pro tapers as the stock ones will break easily.
On your first bike start up make sure to run it in for the first couple tanks of petrol. This does not mean riding it slowly around the track at one speed. You should run the engine hard! At times rev the bike hard and then slow down.