what should l do before l go to Mount Kinabalu? Any procedure before going there...^^? do l have to go to a medical check before l start climbing that mountain?

It is 4000m high so you'd wanna be pretty fit. Not only that but at that altitude you're gonna feel like doing a certain amount of work takes more energy and longer to catch your breath. Be ready for that. l checked wikipedia and it says you should not go without a guide, it also says that it is a relatively easy climb that can be done without climbing equipment.

You need to be fit, and also have good stamina, as you will leave for the final clmb very early (maybe 2am). Therefore, you will need a headtorch (LED ones are lighter and more reliable).
Also, be prepared to suffer the effects of altitude sickness, which can feel like a bad bout of flu; and you can suffer from it no matter how fit you are.
Be prepared to be both cold and wet.