Here are the checks I try to do on my GTS every 2 weeks:-
Battery - Test with voltmeter the reading for A) Engine Off, B) Engine Running, C) Throttle partially open (3000 rpm), at the same time check that the battery leads have not worked lose.
Engine oil level
Hub (Transmission oil) level
Tyre pressures (top-up if required), visual inspection for wear, cuts and any abnormalities
Lights - Running lights, low and high beam, brake and number plate lights
Plus visual underneath inspection for stone chips, rust spots and lose wires (especially around the rear light cluster)
I find the whole procedure only takes around 20 minutes. I know things like the transmission oil don't need checking this regularly, but I think it might as well be done as part of my maintenance routine.
Any suggestions for improvement?