I want to try meditation.how can i start and what to do.what are the principles?

Start now: Positive mental attitude, close your eyes, relax, deep breath thru' your nose slow and easy.

Mindfulness Course: One way is to take a mindfulness-based stress reduction class -- many communities have them, with trained instructors. Search on this site for your location: http://w3.Umassmed.Edu/mbsr/public/searchmember.Aspx also you can get cd's by jon kabat-zinn, jack kornfeld, sharon salzberg, etc. Many libraries have them; also sounds true is a great resource to buy them.

Abdominal breathing: Studies have shown that meditation can have positive effects on your autonomic nervous system, your immune system and your hormonal systems, thus rebalancing your overall metabolism. Proper abdominal breathing techniques are paramount in achieving the relaxation response. You do not need to be a master. Find someone who can teach you this and then practice it consistently.