I do the first way ("read the API/language spec"), and it seem the good way, to me. However, sometimes doing more than one thing may help if needed. But you co

I do the first way ("read the API/language spec"), and it seem the good way, to me. However, sometimes doing more than one thing may help if needed. But you could also try writing stuff to see what it is, and then you can learn by that way, maybe; that would be in addition to reading the document, so that you can know what it is, and see if it is helpful. I don't know how to call myself proficient, so I just guess. If I made something with it, then I might say I am proficient to write that particular program with it.