I strongly suggest “How to Read a Book” by Adler. It’s an excellent discussion of types and levels of reading.
When faced with a large, imposing text, my method is:
1. Read the title page, table of contents, index, and introduction several times. This should make it clear what the book is about and how it’s structure.
2. Read it straight through from start to end. No notes. Don’t worry about not understanding. Intellectually, I’m very passive. Just familiarizing myself with the terrain. Keep in mind the knowledge gained from the previous step.
3. Read through again, paying attention to key concepts and terms. Make a list of key concepts and terms. Try to understand and resolve the concepts and terms in relation to each other and the structure of the text. This is still very passive reading. You shouldn’t be forming any opinions at this point.
4. Create your own outline of the text. If the table of contents is well thought out, this might be redundant. Still very passive. No opinions yet.
5. Go through again, summarizing all the key ideas. Still very passive, you’re just trying to map out the text. Not forming opinions.
6. Rewrite the outline, now including your summaries.
7 and above. Now, if necessary, start actively critiquing. That’s a whole different matter. And usually involves playing the author off other authors. You usually don’t get to this part. I’ll refer you back to “How to Read a Book.”
The key thing is to focus on passively understanding, rather than opinion formation.