Have a crack at every question that comes by in this place--before you look at other peoples answers. Then when your bored with problem, or run out of time, compare where you were going (or got) with what others did. And if you think what you have is a reasonable and a sufficiently different answer to those already posted--post it.

There are such a variety of problems here that it takes you into all manner of interesting areas and modules. Eventually one or two of the problems, or types of problem, will become interesting enough for you to pursue it purely for your own sake.