Welcome to DV!

I'm sorry your dreams aren't pleasant. Learning how to LD to get rid of nightmares is one of the most common reasons. What you need to do is to start visualizing yourself being in danger of any kind, or perhaps if you have a recurring dream or a dream sign of some sorts. Visualize seeing that familiar dream sign and then tell yourself you'll check if you're not infact dreaming. Doing this many times a day will eventually carry over to your dreams. Start questioning your reality and you'll do it more and more in your dreams. If you realize you're dreaming and you're in a nightmare then just change the dream or close your eyes. You'll soon wake up. Don't be scared of ending up in SP. SP is completely natural and harmless and will only turn ugly if you're worried it might happen. Try to think of a nice dream scene instead and ignore what you feel or see.

I had nightmares alot as a kid and I learned how to LD because of them. If you're wondering about something then just ask