Well, for me I find that when I reach the vibrational state most if not all thinking about the actual vibrational process nullifies the vibes almost completely.
Personally I find what works the most effectively is to just relax and think nothing of it during the vibes, just sink into the rhythm; the vibrations normally take care of themselves and if you are fully relaxed and almost nonchalant about it the next thing you will know is that you are floating out of your body.

The key thing's stopping anyone at this point are emotions (fear, excitement.etc) and trying to hard. It certainly is tricky to maintain calm and collected during the vibes but it is pretty much the only way you can intentionally achieve the out of body state.
You are at the final stage of separation so it is literally no more than a subtle intent away or a will to 'go'.

Hope that helps a tad!