There are a few things you can do. If someone adds a comment to your hub, then find their profile and read some of their hubs. Make sure you comment on them, and try to show that you put some thought about their hub in your comment. Then go back to their profile and follow them - on the right side margin there is a box with several option and one of them is "follow "so-and-so". After you click on that it will bring you to a page where there will be a hyper link for you add "fan mail." Click on this and add greeting, just hello, I'm new - or something quick you like about their profile or maybe have in common with them.
Also, see who else is following them - you can do this from their profile. Then repeat the above process with some of those who look interesting to you. Very often, once you follow someone they'll read some of your hubs and follow you.