excitement usually is the problem. but if you find yourself calm and collected before you "get kicked out" then it is probably a stability problem. always make sure you do a reality check as soon as you have te feeling that you are dreaming. then when you know you are dreaming without any reasonable doubt you can start working on your senses. like touching and feeling etc. i always rub my hands. spinning doesnt seem to work for me, especially in my beginning stages of lucid dreaming. dont jump ahead of your self and take it one step at a time. good luck!