Buddhism offers a rich variety of meditation practices. The following basic exercise in focusing attention comes from B. Alan Wallace's The Attention Revolution.
Begin by sitting on a cushion with your legs crossed or, if that's uncomfortable, in a chair or even lying on your back, but always with your back straight and body relaxed. Your eyes may be closed, half-closed or open.
Be at ease. Be still. Be vigilant.
Take three slow, gentle, deep breaths, breathing in and out through the nostrils. Let your awareness permeate your entire body as you breathe, noting any sensations that arise. Now settle your respiration in its natural flow. Observe the entire course of each in- and out-breath, noting whether it is long or short, deep or shallow, slow or fast. Don't impose any rhythm on your breathing. Let the body breathe as if you were fast asleep, but with your mind vigilant.
Thoughts are bound to arise involuntarily, and your attention may also be pulled away by noises and other stimuli from your environment. When you note that you have become distracted, instead of tightening up and forcing your attention back to the breath, simply let go of these thoughts and distractions. Don't get upset. Just be happy that you've noticed the distraction, and gently return to the breath.