From what I've read from literally every author I've read on Astral Projection matters, no; you can't get possessed. Not possible. Doesn't happen.
Some believe that "negative entities" can latch onto you, frighten you or disturb you, even into having effects on the physical plane, but not all; those who do suggest anything from having a personal religious symbol on your bed, to trying some form of Kundalini exercises and chakral cleaning, to simply imagining a "white light" around your body, growing stronger. There are probably many more methods out there, but these are the ones I can recall off the top of my head.
As for Lucid Dreaming, no, absolutely not; that doesn't even make any sense. Lucid Dreaming is just the activity of becoming aware in your dreams, and taking varying levels of control and perceptive command. It isn't necessarily related to anything "spiritual" anyway; possession doesn't come into it whatsoever. :-P