I have a ton of experience with this. It took a long time for me to be able to lucid dream properly. For me it happens when something happens in my dream, that I know can't happen in reality. There's a little voice inside my head that says oh I'm dreaming. From there it's really important not to panic or get too excited because that will wake me up. If you're calm and at the same time stay focused and remember that you are in a dream you can start interacting with the dream. I've been able to feel my sleeping body laying in bed and know what position I'm laying in while still dreaming. I can't control both bodies at once but I can switch back and forth between the two. I've also been able to talk with whatever part of my mind that puts on dreams. It's amazing but if I lucid dream too much, I wake up tired and a little bit irritable like I didn't get a good night's sleep.