once you ride the bike everyday and are used to it, you should be able to feel when something just isn't right.

listen to your bike. it'll let you know when it's not happy!

other than pumping the tires, and lubing the chain (along with an occasional wipedown/inspection) i only do maintenence when i feel or hear something wrong... the longer you ride the better you get at diagnosing these problems by the type of click or squeak it makes!