If someone takes the time to comment on your work, make sure to thank them and respond to what they have said. It's always nice to know that if you take the time to comment on someone's work that they have at least read it and appreciate it! 

You can also ask questions at the end of the chapter to get more interaction with your readers. I've befriended some decent chaps and chappettes by asking for opinions.

Oh yes, don't forget to vote :P

NB: Sometimes there isn't enough time to respond to all the comments, especially if your book has been read millions of times. I do my best but sometimes I can't get to them all.