As I don't know how you as an individual learn best, it would be wise to examine all the advice given above and choose what seems most like the way with which you're comfortable. If you're a very verbal person, and learn well through explanation, then a text would be a good starting point. If you're intuitive, and particularly visual, then just looking at lots of well made work will be helpful. If you learn best by doing, then that's the tack to take. But, since most people employ a synthesis of all those modes, exploring them all, at least to some degree, is probably a good idea. But you need to either be able to articulate, or at least 'sense' the 'rules' before you can break them, and have a clue why you're doing so. Otherwise, you will flail about wildly for far longer than you should and pretty much resemble me as a tennis player; now and then I do something brilliant, but haven't a clue how to do it again, and again. Lessons (from whatever source), constant practice, and the discipline to follow the process through to the end (including ciritiques by people you respect) are the only reliable ways I can think of to move in the direction of mastery.