The traditional position is the lotus posture. However it can be hard at first, but luckily there are other positions.
You require a chair with a firm back, you need to sit comfortably, but poised, with your feet touching firmly on the floor.
Your hands should rest on your lap or knees.
The idea of this position is so you can forget about the body, so you can free your mind.
Ensure the room is dim, but not too dark. A nice warm room is also preferable. It is all about comfort.
Then get rid of ALL distractions, and relax.