Find a quiet place you can sit or lay for a while undisturbed. For for the sake of example I'll say sitting and in your room. Ok. So sit on your bed. Sit however is comfortable to you. If crossing your legs is better then do so. If spreading them stretched out is better then do so. Now relax your body. Release any tension you have. This may not work all at once so do a breathing exercise. Breath in heavily and slowly; count one. Exhale slowly; count 2. Inhale deep and slow; count 3. Do this until you get to 10 then start over at 1. As you do this you will notice your breathing getting softer and slower. Your body getting very relaxed. Your mind getting clear. And that's what you want. Your body relaxed and mind clear. You may not be able to completely get your mind cleared on the first try but with practice you will get it done. You can meditate for as long as you want. How long you meditate is up to you.
Many people may suggest to inhale through your nostrils and exhale through your mouth, but not every one can accomplish doing so. It really does not matter. What matters is what works for you.
When meditating laying down there is a chance you can fall asleep during meditation. If so then that is fine. Meditating laying down is a very good way to help induce sleep.
When meditating indoors it's also helpful to play soft, soothing music such as nature tracks. Various other musics such as trance, isochronic tunes, and classical music may help induce relaxed, clear minded meditations or even a trance-like state.
Seems complex but it's very simple.