Ryan Budney and Andrej Bauer cover most of what I would say, but I would add:
Spend a couple of hours a week reading some Wikipedia article about a piece of math that you have heard of but don't understand. Follow the links when you see an unfamiliar word. You will know more that when you started even if you are still uncertain about parts of it.
I hope you have one or more friends you can shoot the bull about math with. Then talk to them about the article you read, get into arguments about it, talk while taking a walk with them, and so on.