I have a two point plan that works very reliably:
1. Keep up with my dreams, think about what the landscapes of my dreams look like, and be ready to recognize the dream realm when I am there.
2. Try often to float straight up. Obsess over it. When I can finally float up, I know that I am definitely dreaming.
When you become lucid, stay calm. Getting too excited will wake you up. If you want to control your surroundings or your actions, visualize what you want. A dream is just what you are thinking about while in R.E.M. sleep.
If you want to keep a dream journal, I recommend a tape recorder for reporting your dreams after you wake up. You can say stuff a lot faster and record a lot more before the memory fades significantly. You can play the recordings later and write them down or type them.