Aside from reading tutorials and trying to make original programs using a certain API, what are some tips that can help me effectively learn an API (OpenGL in my case). I am thinking of keeping a notebook or notepad file of function prototypes, does that sound like a good idea?

I would prefer that no tire kickers who do not know an API (win32, directx, opengl, etc) answer this, it is indended for people who already have experience and have some helpful suggestions that worked for them.

Ok thanks in advanced!