This is just from my personal experience, but I find the best way to really learn the material is through repetition.
Read the material, try to derive the results yourself (don't just look it over), work on problems.
And here's the key - after a time, reread the material, go over it all again. I find that often after I first learn a topic, it takes a while for the ideas to settle and for me to grasp them fully. After a time, I go back again and relearn it from a fresh perspective and it makes much more sense and I'm able to pick up on more details I didn't realize the first time.