Well, you may not have any HI (Hypnagogic Imagery) at all! Some people (like me) only gets the vibrations, but then you must stay calm, think of nothing and try to imagine a dream scene. Ignore strange feelings, just keep focusing. If you lose your focus, try a variation with the Suneye:
[url]The BIG Suneye Topic - part II]
I’m far from an expert, so it might not work, but it’s worth trying 