Oh, I dunno about sleep position, but there is plenty to learn about stabilizing and prolonging lucidity--look around the forums here. Different things work for different people, but in the longest LD I've had to date (about 10 minutes or so), I started by touching everything I could reach once I realized I was dreaming.

I think it does get easier after the first time, in that you know for sure you have this capacity. There may (or may not) be dry spells, but you for sure are able to do this, and you will again.