Regard all of math as a tree based on essentially depth. Right, this is an over simplification since really have a directed graph of dependencies. But cheat a

Regard all of math as a tree based on essentially depth. Right, this is an over simplification since really have a directed graph of dependencies. But cheat a little and get a tree. Then study the main trunk and larger branches. For the deep roots, that is, the foundations, go light on those or will get confused, discouraged, and generally stuck-o. E.g., do some axiomatic set theory if really want; see some of the axiom of choice, but go light on the latest material on model theory and forcings. Then with the trunk and larger branches, will be able, as circumstances require, get to nearly any of the leafs fairly quickly as required. For that ~2000 page PDF, there, too, try to find the trunk and larger branches and mostly skip over the leafs. Maybe 80% of that book is leafs. Finding the trunk and larger branches in that book could be challenging. So, instead, just stay close to the commonly recommended undergraduate math major texts and topics. For each such text, at least glance at the 2-3 leading competitive texts and, then, take what is in common as the trunk and larger branches. Also for each topic, pick the best looking treatment and then glance at the other treatments. If you can, find a really good math prof in a really good math department at a really good university and try to chat with him about your progress for a cup of coffee (you pay) hopefully 4 times a year. If you can find more than one such prof, even better. Some departments publish their old copies of their qualifying exams; might get some of those! One more: Don't let yourself get stuck or discouraged. It's a fact of life that not all the materials are good. So there are some actual errors. Some exercises are just too darned hard, need material presented later in the book or not at all, or are just tangential curiosities not worth the trouble. Some of the writing can be obscure. Often there is not enough motivation to let you figure out what is important and what is not: If really obscure definition X or theorem Y seems not to be used in the rest of the book, then find some good reason to study X and Y or maybe delay them or just skip them. Sometimes obscure X, Y actually are important; sometimes not. There should be motivation, but commonly there is not. If you can't after a good effort understand something or solve an exercise, don't assume that the difficulty is you or that you are leaving a dangerous hole in your knowledge. If later you decide you need that something, then return and give it another shot. Generally for a really good, mature view of a book, just need more than one pass through it; so don't seek everything on just a first pass. Even given a really thorough first pass, you will notice significantly more on a second pass, e.g., some later material on the first pass will help you better understand the real points and importance of some earlier material on a second pass. And do glance at some alternative treatments. One recommendation is to chew on a proof until you really see it thoroughly. A counter recommendation is just to notice that we are all short of time. Net, use some judgment.