I don't think it's all that important to have
one particular mentor that's sort of a formalized relationship. I do think it's important to surround yourself with people - preferably in a face-to-face environment, like a job or coworking situation - that have done this before and have a bunch of experience in development. Observe them carefully - not just the product of their programming, but the process they go through to create it.
I disagree with the poster who says Google is your mentor. Google's great for sticky questions that nobody knows the answer to. But Google will never tell you that you should be asking a question but don't yet know that it's a question worth asking. A lot of things in programming are like that: you'll see someone do it and think "Why didn't I think of doing that?", but the reason you never thought of it is because everyone who does it considers it too obvious to be worth blogging about.
