Get ready for this...

If you're behind the bike, looking at the RD, the turning the adjuster in (Ie, counterclockwise) adjusts the RD toward the big ring of the cassette, and turning it outwards (Clockwise) adjusts it toward the small ring of the cassette.

Usually you'll be able to figure out which way it needs to go by noticing whether the chain is wanting to stay on the big rings when you are shifting down, or vice versa. Adjust to compensate.