In my first year of a doctoral program, I could study from after lunch until next morning and I concentrated on getting the fundamentals right. The greatest book, the one where things began to click, was Rudin's "principles of mathematical analysis". Before I came to this book, I had wasted a lot of time finding my style of learning or, if you will, discovering my preferences. But if you already have the basics and are not going to waste as much time as I was trying to figure out what is what, you might pull it off much quicker.
Good luck! To me it was a cool time and I finally got rid of my math inferiority complex ;)