There are three basic things you need to do – clean , lube , and check .
Clean your bike when it is dirty. Although it is good to clean your bike because a clean bike looks nicer, dirt can cause corrosion and wear on the moving parts of a bike, especially the chain. Do not use high-pressure washers though, bike bearings are not made to withstand high pressures and so the bearings will get damaged.
Lube . After cleaning the bike, you should always lubricate it. The parts to lube are the front and rear brake pivots, brake lever pivots, rear mech jockey wheel, rear mech pivots, front mech pivots, cable ends, and the chain. If you are not sure what these parts of the bike are, it is anything that moves apart from the wheel bearings themselves.
Check your bike to make sure nothing is loose. Make sure that the pedals and their cranks do not move too much when you try to pull them from side to side. Check also the saddle is still tightly fitted and will not twist. Lift the front and then the rear of the bike and spin each wheel. Watch it as it turns to make sure it does not wobble or move from side to side. Also make sure that the brakes do not rub on the side of the wheel rim. If a repair or adjustment needs doing that you are not confident to do yourself, either find someone who you can trust to do the job properly, or take it to your local bike shop.
