In my opinion, technique wise, you gotta adjust the way you grip your pick such that you can alt-pick more smoothly without those interruptions. Personally, I grip my pick between my thumb and the middle of my curved second finger. It gives a more stable grip and prevents the pick from moving, and exposes as little of the pick to hit the strings. I'm not quite sure why but it helps.
And of course, practice a lot. Smooth alt-picking takes a while, but once you master alt-picking, it really becomes terrific fun. If there's one thing about metal guitar that I love, its gotta be alt-picking.