What I do, and it's a very short list:

Before each commute:
Spin the wheels, watch & feel the tires, try to find things poking into the tires
Check for wheel hub, crank, headset play
Inflate to the desired pressure
Charge battery for lights
Refill water bottle

As needed:
If chain has been sounding crunchy, I apply chain lube
Brake and derailleur adjustments
True wheels as needed

Every few months:
Clean chain. Before I do that, I use a Park chain measuring tool it see if it's worn out.
Check wheel bearings for play or rough, gritty action: service if needed
Tighten cranks

Wash bike immediately if ridden in the rain

That's about it... boring and simple, huh?