I think that as long as Federer is around and healthy he will not let roddick win any grand slams. But there are things that roddick can do to increase his own chances of winning. Lets list them:
1.)Roddick should not take long big swings (only when necessary)
2.)Play doubles whether its competitive or exhibition(doesnt have to be on tv)-this will develop his volleying game.
3.)Roddick MUST not rush into serving, he should slow down a bit. (i believe roddick might be trying to get into a rythm or gain momentum when doing that, but its just going to make things worse)
4.)Work specifically on his RUNNING backhand not just backhand
5.)Have a sneak attack at the right time (i think he has that already)Connors is also helping him with his backhand. Looks like its working.
6.)DO NOT flick wrist that much when hitting "SHORT" balls. Too many easy SHORT balls are missed simply by flicking his wrist.