just some few things to check before adjusting the cable

make sure your shifter is completely upshifted so it would be in the smallest cog
check the limit screws by hand (use your hand to move the derailleur all the toward the largest cog)
make sure that the cable is being routed through the derailleur and pinchnut the proper way (straight through)
i'd back the barrel adjuster on the rd itself all the way out (allowing you to tighten it when it turns, rather than loosen. you can always stretch a cable a bit if you need to, i've found)
and then pull the cable so it doesn't move the derailleur (to do this, i usually pull the cable tight so that the derailleur moves and then let it slacken just a tad)

make sure all of the housing is situated into any ferrules correctly.

a great tool for this and any cable adjustment is a set of cable stretchers. the pedro's set is cheaper, but i think the grip on the park one is much nicer and allows for a stronger grip.

good luck with it!