I tend to get sleep paralysis when I am undergoing an usual amount of stress. The last time (a few weeks ago, actually), I experienced a spirit behind me speaking with a saw blade like sound. It seemed to vibrate the universe. He called me stupid because I was interpreting things in a dream a bit differently than he was, I think. Having had many of these experiences, I have gotten good at raising my vibration to get awake. I have also taken the opportunity to go astral a few times. I've seen a few entities. Very few were ever nefarious in any way. In fact, I would say that I've only encountered evil once or twice. Even in real life, I rarely even see (for very long, that is) people with low vibrations. They tend to get annoyed at my not coming down to commiserate and leave.
Anywho, I've found that sleeping on my side seems to prevent sleep paralysis, as does reducing stress, sleeping regularly and enough (biphasic 1.5/4.5 for me), and staying away from too much caffeine. Watching scary movies is out of the question for me in general, but I don't think that they have any effect on sleep paralysis. In fact, I rarely even have bad dreams. Instead I seem to live several parallel lives in my dreams and receive knowledge and advice on a variety of subjects. I just wish I could stop talking about myself so much.