Help with astral projection?

if your going to try to tell me astral traveling isn't real than don't bother i've spontaneously done it before. However now i'm trying to do it on purpose and i can't. I can always get into a sleep paralysis and then my whole body starts to vibrate and tingle but i can never get out of my body. i've tried the rope technique, "rolling" out of my body, floating up, or just imagining myself at a different location and nothing seems to work. why can't i leave my physical body? any advice from people who have actually achieved astral projection would be greatly appreciated.