Use new combos often and intelligently. Using a new combo every few beats wouldn't make sense, but you also want to avoid long combos that continue for many measures. New combos should also be used to show changes in spacing such as jumps.That last sentence?
I'm sorry, but it's bad advice for today's mappers. Nobody nowadays goes, "Oh hey, there's a New Combo... there might be a jump here!" In fact, I haven't seen anybody use NCs for jumps in years, because it doesn't help anybody and just makes your map look ugly.
Please delete it, because seriously, nobody does that anymore. All you're doing here is making it so some new mapper will get a lot of "Remove NC's" mod posts because they followed this guideilne. ;P