Here is my "schedule" (on-road, no-dirt bike).

Check tire pressure once or twice week and also before each really long ride.

Clean and lube chain every month or so.

Occasionally (when I happen to think about it and realize I haven't done it in a while) check bolts for tightness, brake pads for wear, wheels for trueness, chain for stretch -- and fix whatever needs to be fixed.

Do a major cleaning of the bike once a year and more local cleanings when the bike is dirty and I am not too lazy to do something about it.

Other than that I just fix whatever obviously needs fixing, e.g. sloppy shifting, loose brake cable, funny sounds from any part of the bike. Recently I even straightened a bent derailleur cage! Well, I helped anyway...