Back sleeping is the best way to sleep because it keeps the spine in a neutral position. If this is difficult, place a small pillow under your knees or low back to keep pressure off the low back.
The next best position is side sleeping, with your neck properly supported by a pillow. Keep in mind that the hips should also be in a neutral position and placing a pillow between your knees will help maintain alignment.
Sleeping on your stomach is not recommenced.