I myself have trouble falling asleep as well. I have had nights where it has taken me 2 hours or longer to fall asleep.
The biggest tip of advice I can give you is to not think about lucid dreaming at all when you go to sleep. Just lay there with your eyes closed. Let thoughts come to you; forcing thoughts will keep you awake.
I also find that running at least a mile a day helps with it. It helps separate the tiredness of your mind and body.
