Sleeping position should not have any effect on dreaming or lucid dreaming. Although buddhist monks say, that females should sleep on one side, and males on the other. But for us, common folk, it doesn't play any significant role.

The goal is to fall asleep, so you should be in your comfortable position.

Induction Methods and Techniques - please check out these tutorials to see what you could be doing differently. Then ask your specific questions, and we will be happy to help. Happy dreams