Vibrations are one of the signs for both WILDs and APs/OBEs. If you want to enter LD, I think you wait for images/dreamscapes to form behind closed eyelids and then enter the dream. If you want to AP/OBE, during/after feeling vibrations, think yurself to hover over your sleeping body. It happend to me only a few times, so maybe someone more experienced will answer. Happy dreams