Adding on to Sageous' post (which is dead on), energy plays a very big role in lucid dreaming. If you think you can't, then you can't. If you think you can, you will. It may take time, and it may grow slowly, but you will.

You want to set a positive energy flowing when you think about lucid dreaming. If you feel yourself getting down about it, take a break and reassess. Read a new book or an old favorite (ETWOLD). Get yourself motivated again.