The first, and most important, step is to identify someone you'd like to become your mentor. Look for the following characteristics.
Your mentor will likely be older and more experienced than you. Make sure he or she is experienced in the areas you want to learn.
Your mentor should have a good reputation and the respect of others.
These are things you can tell with a little research. You may be able to get an idea about the following characteristics, too, but sometimes you just have to guess and go.
Your mentor should be able to explain things well. Not everyone who can do something well can explain how it's done to others.
Your mentor should be willing to be a mentor. He or she should enjoy the process of helping people learn and succeed.
What about race and gender? Should my mentor match up with me on those dimensions? Yes, if the other characteristics are there. The most important thing about having a mentor is mining that person's knowledge and experience.
Now, once you're identified a potential mentor, what do you do? Approach them. If they're willing, then meet with them a couple of times.
Successful mentoring relationships depend on chemistry. It's either there or it's not. If not, try someone else.