I tend to not reply to comments and/or favs. Because I generally don't have anything to say about them. This doesn't mean that I don't appreciate comments and/or favs, just that I wouldn't know how to respond if I were to respond.

A good way to get me to answer a comment is to either A: Offer some advice on how I can improve, or B: Ask a question about the picture. I tend to not answer comments that say "Good work" or "I like it", because what would I say?