I experience the spins often when I'm drifting off to sleep, but nothing ever happens.
Does anyone have any advice on what to do once the spinny/vertigo sensation is achieved in order to successfully project?
Based on some theories I've read it could mean you are achieving a projection but your consciousness is not shifting and your memories are not downloading to your conscious mind.
So you've projected but can't recall the experience of your astral projection. Do some mantra work to tell yourself to remember your experiences, and try to tell yourself to do something during the experience that is memorable. Also tell yourself to keep the projection for only enough time to just look at yourself and jump back to your body. The shorter the OBE, the more likely you will remember it.