Make sure that the stem is clean inside with no pointy bits of metal waiting to stick into the carbon.
Then make sure you have the stem at the correct height - with either spacers above or below - and that there is 1/4 inch of spacer/stem above the end of the steerer.
Basically you then just tighten up using the top cap (but with the stem loose) and check for play by rocking the bike with brakes on. When you are satisfied that there is no play and the bars turn smoothly simply tighten up the stem.
Don't go overboard with the tightening of the stem as this can scar the carbon steerer - tighten up until it feels nice and snug and then tighten up a tad more.
That's it!- but keep a watch for any play that may delevop as the continued braking/rocking causes wear to the steerer as the compression ring rocks back and to.
