I learned from a previous batch to keep it steady and just turning over. On said batch, I had a pretty vigorous boil and when I went to add the hops... well let's just say I'm still cleaning hop residue and charred malt extract out of my burners and stove. Funny thing is, even though I lost about a gallon or so of wort, that beer was my best homebrew to date. All my friends have asked for it again. (It was a witbier).