Sleeping on the left ensures proper blood supply to the baby and also keeps the heart healthy.
Sleeping on the back puts the entire pressure of the baby on your organs while sleeping on the stomach makes it terribly uncomfortable.
Get pillows that are specifically made for this phase. They lift and rest the right parts of your body.
During pregnancy the bladder gets weak and makes it difficult to hold urine. So you must avoid drinking 2 hours before sleeping or else you will have to frequent the loo the whole night.
Different trimesters mean different sizes of the abdomen and different comfort levels. So position yourself accordingly.
Wear loose clothes and give your body enough breathing space while sleeping.
Keep your mind free of all worries and try meditating before sleeping.