Trying to achieve Sleep Paralysis/OBE/Lucid dreams

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I've had two lucid dreams, both of which were thanks mainly to this forum. Both occasions were a couple of years ago and I haven't really been very disciplined when it comes to reality checks, practicing etc. The phenomenon of sleep paralysis/OBE's sounds very interesting to me. After reading some guides on here last night (lye down completely still, ignore impulses to scratch itches and turn over), I tried it. I was pretty good at ignoring impulses, and after a combination of trying to just think about weird dream scenarios, keeping still and ignoring impulses, I got that weird energy that waves over your entire body, but then... nothing. I tried this numerous times in one night and I did get the wave of energy several times, one time in particular was very intense, but nothing else ever comes of it. What am I doing wrong? I'm assuming it's to do with what I'm thinking of, because my thoughts are usually split between trying to dream, trying to stay stay still and anticipating the wave of energy.