make sure you clean the air filter allllll the time. I neglected to do this with my first dirtbike and eventually all the debris that got by scored my cylinder walls and seized the engine, it had to be rebuilt completely.
I have been told to use an outerwear for all filters as it will help to prolong time between filter cleanings. I was told to have a couple on hand when I go riding so that the can be swaped out when they get covered with dust and dirt. I have not had one long enough to do this but I thought that it might be good info.