Being farely new to deck landings myself, I'm not too sure if this advice will benefit or is even correct, but I was giving the following lesson that seems to work if the deck is moving at all.
As I started to come into the hover over the deck (it was near our SOP limits for pitch, roll and heave) the Captain asked me to watch the deck. Of course using the deck for reference soon had me overcontrolling and all over the place, and that was the point of the lesson. Watching the horizon and monitoring the deck though my periphral vision worked much, much better, and allow the deck to move around below you, timing your landing as in the above posts. And if its dark and low vis, I've found you can sort of look through the ship, to its imaginary center, and use that as a point of reference. There always seems to be a lull in the movement as well if you watch for a pattern. Do you fellows with alot of time doing this sort of thing agree?
I get green as well if I spend too long on a heaving deck, and it seems much worse in low vis/ heavy rain/ fogged up windows....
I don't know how you Navy types do it.