I found that making a "thanks for subscribing post" on someone's wall along with an illustration of some sort has been great for getting sorta generalized feedback from your readers, and people really appreciate it too. Besides that, just responding to comments is always a good thing too.
Definitely don't wait til you get more subscribers to interact with your readers, in fact the "thanks for subscribing" thing becomes harder to start doing the longer you wait. On top of that, I found that when I was just starting out the quality of my interactions with readers was a little bit better and more personal feeling, because there's this level of like "Oh man I've discovered something really cool that no one else knows about, I'm gonna be extra supportive" or something like that? Not to say that my current interactions with my readers aren't great or anything, but it's definitely different to how it used to be.