Sometimes, if you want to develop your skill set further within some field, the best method can be to impose some artificial restrictions that will force you to step out of your old habits, form new creative ways of looking at the activity, and learn aspects of the craft that you’ve earlier been able to ignore.
For example, let’s say that you want to become better at composing music. So far, you’ve always worked within a modern sequencer hooked up to a midi keyboard. You’ve spat out a couple of okay pieces, but you have no idea of the underlying structure of them, why some things worked and some of them didn’t, or which type harmonies that goes good together.
Well, how about forcing yourself to pay attention to these details. For example, you could abandon your fancy music program for a much more basic and bottom-up tool like LilyPond, a programming language for typesetting music scores. While you’re at it, chuck your midi keyboard into the closet. Now try to compose.
I challenge you to do this, create a couple of pieces, and not come out on the other side with a much more deep knowledge about composing and music theory. It happens, almost automatically, because you’re throwing away your crutches and forces yourself to try walking without them, even if it will mean that you’ll fall over a couple of times.
Find an area in your own life where you’ve almost stagnated, and find out what you can do to make the activity harder and more rewarding at the same time (and also, which comes with the territory, more frustrating).