I use sand paper, don't have a buffer myself, a little bit of hard work, going through the grits, 400 (for deep scratches ahem... Doug), then all the way to I think 2500 grit I used, then finished it up with a novus 3-2 punch.
I did have a scratch kit that had all the way down to 15000 grit I think, which is a good thing to use on a full tank since that'll get that the last bit of haze away and you can't exactly use novus inside the tank.