Build something. Anything. Small or big, doesn't matter.
Just build - in your free time. If you don't have free time, make time.
What to build? Pick something that you wish software/hardware did, but you don't know any that does.
I cannot upvote this enough. When I was getting started on rails years ago, I found it hard to make headway just making headway on a project I got dropped in the middle of.
It wasn't until I decided to migrate a personal project of mine from php to rails, and had to set it all up on a VPS with Phusion Passenger, all by myself, that I made that order of magnitude jump in skill level from novice to intermediate dev. Having that side project has also let me try out so many different things I could never be able to try out at work without know if it would work or not.
Those countless hours you spend off the clock screwing around with something just because you want to is simply invaluable to your progress as a developer, this is why to this day, I keep an eye out for developers that find time to hack on side projects.
