drink LOTS of water. at least a gallon a day.
Also, a lot of it depends on the creatine. The one I used to use gave me all kinds of stomach bloating, damn near gave me love handles single handedly. But I've been using ON Creatine Powder for a few months (i'll get off of it every two months or so for two weeks, and then start back up again) and the bloating isn't as bad, while still making my arms feel fuller and reducing recovery time.
Truth be told though, there's probably no right answer. One of the side effects/purposes of creatine is that you'll retain water weight, which makes your muscle appear puffier. Unfortunately, that goes for your core muscles, as well.