Make Hubs which are controversial. Something, which people actually want to state their personal views about, and be able to share their intelligence/wisdom about. Everyone likes to be able to talk about something they have wisdom in, therefore finding those topics which spark that wisdom will get you those comments!
For instance, my most commented on Hub is one about getting more views on HubPages, and almost everyone on HubPages has some insight into that.
Edit: I've just realised that I've made a bit of a blunder with my answer, as what you're asking is how to increase your commenting level not the amount of comments you get. Maxravi got the information spot on here!