Light: make sure the batteries are fresh. Rechargeables work
well, but have a spare set for each light. At night your cycle MUST have a working front white or yellow light and rear red light.

Tyres: check for worn tread, cracks, tears or holes and replace
if necessary.

Brakes: check pads for wear and tear. Make sure they line up with the wheel rims. Adjust the brake cables and pads so that the brake levers don't touch the handlebars when gripped, and the gap between the pads and the wheel is about the thickness of
50 cents.

Chain: keep it clean and oiled. If it seems loose, adjust the rear wheel tension if you know how, or ask your bike dealer to do it.

Gears: keep them clean and oiled. If they need adjusting, follow the instructions in the bike manual, or ask a bike dealer to do it.

Wheels: check for straightness. If a wheel is distorted, have
it replaced.