As and when needed, if theres no more than dust it just gets a bit of lube on the chain. But on average……….
Hosed down after every ride (no point starting a ride with 5lb of dried on mud!), chain and moving parts get a drop of oil/grease, mech's sprayed with TF2/GT85, rims (v-brakes) degreased, grass pulled out of cassette. check tires for thorns, selas/boots for cuts/leaks
Every other ride:
chain in a jam jar of solvent (petrol, WS, Diesel etc)
cassette scrubbed
Every week:
Cleaned totaly from top to bottom, bolts checked for tighness, fresh grease behind seals/boots, frame checked for cracks, seatpost removed and a bit of cloth wedged in the frame to mop out any moistrue, grease on seatpost and re-fit.
Every 3 months:
Strip bike into parts, and re-assemble with fresh grease.
Bit of a ball-ache, but I'd rather 20min a week in the garrage after rides than a mechanical in the middle of nowhere in the rain.