Change your oil and filter regularly. Clean and oil your air filter often. Check and adjust the valves. Keep the rear chain adjusted and oiled. Sit down and read your service manual from cover to cover. Read it again. Have fun. :cool:
Ol'89r nailed the answer right on the head. Read the service manual, then read it again. It should give you some type of service schedule to follow. Remember, no matter how well you maintain a bike, parts will still wear out. However, by following a proper maintainance schedule you will be able to help alleviate most of the break downs caused by poor maintainance.
One last thing, always go by the manual (or advice from a certified mechanic) and not by "word of mouth" from some half baked yo-yo spouting information like they know it all, when all they really have a grasp on is wiping their noses, and keeping their shoes tied.
PS: The only dumb question is the one never asked........
That should be in the maintenance section of the owners manual. There are several products that you can use to clean the air filter, I recommend PJ1 Aerosol cleaner for it's ease of use. Then oil the filter, there are instructions on the back of the bottle. The chain adjustment typically involves removing a cotter pin from the axle, losening the axle nut, tightening or loosening a bolt on each end of the swingarm (although the TTR125 has a cam that you turn) then tightening a locknut, torqueing the axle nut and reinserting the cotter pin. Don't forget to lue the chain.
These things should be checked at least every time that you ride. If you take care of them when you finish riding then the bike will be ready the next time you want to ride. Also, I recommend purchasing 1 or 2 extra air filters so that you can just change it when needed and then clean the dirty one when you have time between rides.