I reckon that the best way to become a generalist is a two-step process:

1. Become a specialist

2. Become a generalist

This has two advantages. Firstly, you'll be useful and employable in your youth, since a specialist with a few years' experience is a valuable asset, but a half-baked generalist is pretty useless. Secondly, and more importantly, you'll know what it's like to really understand a subject, which should help you in your quest to partially understand all the others.