First of all there is no substitute for practice. Whatever techniques you choose, they should be tried at least several times a week, if not every night. I found that after practicing for several weeks that I would naturally awaken about 3 AM, and then was able to make an attempt. This worked well for me, because it is very quiet and undisturbing. You may OBE immediately, or it could take months, but it will have the greatest chance of happening with diligence and perseverance.

Second is intention. Before bed each night, repeat to yourself with clear intention, "I want to have an OBE. I want to exit my body." Repeat this 5 or 6 times, and then go to bed. This will set the intention in your subconscious. As you make your attempts, this intention will always be in the back of your mind without you having to think about it which will be of immense help. Later on, you can use this technique to set the intention for specific OBE goals such as meeting your guides, projecting to the astral plane, travel to a distant place, etc..

Third is relaxation. It will be very difficult to have an OBE if your body is riddled with stress. Each night as I began my attempt I would start with my feet, clenching them and then completely relaxing them, then my calves, then my thighs, etc.., working my way up my body all the way to the top of my head. You can find more detail about this on the net.

Lastly is the actual OBE technique. For me, it was all about dissasociation with physicality and my physical body. I would lay on my back and begin breathing very deeply. I would inhale very slowly, then exhale in a quick relaxed rush. This would actually give me the sensation that I was falling. I would increase that by imagining I was falling into infinity. I would imagine my bones were turning to jell. I would look at nothing, but focus my eyes on a spot a few inches in front of my forhead. I would otherwise totally let go of all physical sensation, totally surrender my body to float away. I wouldn't actually think of anything, but let my preparations and technique take their course.

Other techniques work for other people.