I am a natural lucid dreamer and the way i start my dreams is to think of my day,if i want to dream about it, or past dreams i have had and if i want to dream them again or make changes to them.i think of these things until i fall asleep then i sometimes remember i am dreaming.In the morning i wake up and if it is still early i try to remember what i just dreamed about and fall asleep being already lucid.i don't know if that is explained very well or if it will help anyone but if it does please tell me.(don't think about it too hard or else you won't become lucid!)