Well, from what I have figured, the feeling of being is stuck is because you are actually feeling your "astral body" and it is not moving / you've not gained perfect control of it.
You could try closing your eyes and simply imagining your body float out a bit by bit like a gas or water, if you are in sleep paralysis; but my description is pretty vague.
Perhaps this would be the best way, from my personal experience: imagine walking on a really tall skyscraper, seeing a skyline in early morning. Come closer and closer to the edge of the building. Visualise all of it in as much colour and detail as you can. You walk near the edge and look down - yellow taxis are commuting passengers through the town and miniature people are walking on the sideways. You simply walk off the building and feel rapid acceleration towards ground. You speed up more and more, but don't get to the bottom for a while, because the height of the skyscraped is very large. In a few seconds, you see windows of buildings coming closer and closer and relatively speeding up as you go down. Time stops. Nobody is moving except yourself. You reach the ground and feel your body push away from you, as you still are accelerating downwards. Visualise the collision as strongly as you can, and try to feel it.
This might work for you to astrally project. This method was the most successful method for my experiments, where I almost projected, but freaked out.
Imagining any scenery and big heights always helps, from what I read. Just keeping your state as long as possible will enhance next attempts (not many people succeed quickly): some people get it in 10 minutes, some may take as long as two hours after twenty attempts.
You can further improve such experiences by altering your sleep a little: go to sleep at 11pm, set your alarm for 4am and do something that would make you stay mentally alert, but not physically (your body should be quite tired, still) and then attempt such a scenario / relaxation. The important aspect is keeping your mind alert and your body tired.
I'm a bit vague and am sure you could read more on the internet at lucid dream forums and such.
Good luck! Keep me posted, I want to hear if you succeed by any chance.
Now I want to try this, as the last lucid experiences I had were about two years ago.