When I am lucid, if I concentrate on doing something too much, such as flying, conjuring or anything not possible in real life, I lose lucidity/vividness or even wake up altogether. Why is this?
Concentrating too hard means losing the bigger picture, which is tremendously important in dreams. Learn first to be constantly aware of your surroundings and your situation (that is, you’re dreaming). That will enhance your lucidity and the
stableness of the LD. Then you can focus on developing dream powers. If you immediately try to use powers, it’s like trying to build your boat house on a raft instead of a proper large boat.
Dream powers come with confidence and visualization, not with effort, particularly physical one.