TITLE: How and when to do exercises from books?
QUESTION [9 upvotes]: Most math books I have seen seem to be structured in the same way; each chapter is a few dozen pages, and after each chapter there are a few dozen exercises. I often find myself not knowing what exercises to do and when to do them. If I have read the first 10 pages, I'm not sure what $x$ is in "the first $x$ exercises should be answerable after reading the first $10$ pages." 
A prime example is Tristan Needham's "Visual Complex Analysis". It's a very good book; however, the first chapter is about $50$ pages long, after which follows a splatter of $50$ exercises. I'm not sure when I should interrupt my reading and go the exercises. And I'm not sure when to interrupt my exercises and go back to the reading.

REPLY [2 votes]: As has already been discussed in the comments section to this question, any answer to the question will be subjective and opinion-based. What's always important to keep in mind is that methods that work for some will not work for others. If I had to give one piece of advice, it would be find out which method works for you. That said, here is how I approach these types of books.

In general, I prefer to completely finish the reading before starting the exercises. I do this because I want to make sure I understand the material covered, and for me, the best way of doing that is to do an assortment of problems on all the theorems and ideas covered. So, for example, suppose the chapter talks about Theorem A, Corollary B, Theorem C, and Theorem D. If I were to do the exercises concerning Theorem A and Corollary B immediately after reading about them, I would probably forget about them after I have finished the reading (and done the exercises) for Theorems C and D. So, instead I finish all of the reading and then do all of the problems. Then, I review the problems that I am unable to solve and the theorems, properties etc. concerning them.

This method works best with shorter chapters or sections (no more than 20 pages long). For slightly longer sections (like the 50-page sections you mention), I like to read some of the chapter and then do a sampling of exercises before completing the reading. So, for your case I might read 20-25 pages, then do 5-10 of the first 20 exercises in the exercises section just to make sure I understand the concepts that I learned in the first half. Then, I would finish the reading and solve all of the other exercises. I find that this method works very well with longer chapters (as long as there are sufficient exercise problems, which in your case is not a problem).

To further reinforce my understanding of the topic, I like to circle questions that I answered incorrectly the first time and then come back to them a couple of days or a week later. If I am still unable to do the question, I circle it a second time and reread the relevant theorems. I repeat this process until I understand the question and the relevant concepts.
Hope this helped! :)