I think it really depends on your read of the serve and when you commit to the forehand. It's almost like cheating to one side because its the positioning that really opens the way for the power/winner. You have to start moving moments before the server hits the ball. Specifically when the server takes his/her eyes off of you and looks at the ball (essentially right before he/she hits it). Anytime before that and you possibly reveal your intentions to your opponent and subsequently get burned.
So, during that time take a few side steps toward your backhand and then make the usual split step when the server hits the ball. Another thing you could do is a split step with a bit of a lean toward the left to give you that extra bit of movement/positioning toward that side.
If you want an accompanying video then here's this http://www.youtube.com/watch?v=p3FuR...eature=related
. In this you'll notice that Federer starts cheating to his backhand before the serve is hit by taking a few steps, then he leans toward that side, splits, positions and hits the forehand.
If you want instruction on hitting it, then I'd say try to end the point with a winner by hitting as cleanly as possible. This is a really aggressive maneuver, so at a minimum hit to a really uncomfortable spot for your opponent. Otherwise, you'll be out of position and get burned. Personally, I'd aim for an inside-in forehand down the line. End the point by taking the quickest path to the fence (after bounce that is). If not, then my final advice would be to hit the ball right on the sweetspot. I think the combination of your swing + serve pace + sweet spot should at least give you a fairly pacey/aggressive shot to work with.