Talk to them. Don't grovel; simply sit or stand, whatever's comfortable for you, clear your mind, turn your attention to the deity as you imagine him or her, and talk as you would to a much older and wiser friend. When you're done, remain silent for a time, and then do whatever.

Have you by any chance read The Weird of Hali: Kingsport, the second of my tentacle novels? The way that Jenny prays to the Great Old One Tsathoggua, and her experiences with that practice, are based on my own experiences praying to pagan deities.