This is the first part in a series on how to read books. That pretty broad, so I'll narrow it. :-)
More specifically, this series will help you:
1. Figure out how to pick good books to read
2. Arrange different types of books to maximize different reading opportunities
3. Interleave different books to maximize interest and retention
4. How to easily take notes
5. How to increase your reading speed
To begin, I'll establish a few reasons why I might know something about all of this, though I'm by no means an expert: I read a lot. :-) Here is a link to my Goodreads profile. I read an average of 60 books every year. This year I've read 39, so I'm on track to read 90-100 for 2018. That's about 35,000 pages/year, or almost 2 books each week, totaling 700 pages. This DOES NOT mean that I remember everything I read (I don't) or that everything I read teaches me a lot about something. It does mean that I have experience in the field of reading-a-lot. :-)
The first step in any reading process is the question: What shall I read?
Here is the short answer: Whatever you want! Seriously. It is better that you read Harry Potter than NOT read Leo Tolstoy. Better that you read "The Introductory Summary to the Basics of..." than NOT read "The In-Depth Guide to Deep Specific Stuff". Better to actually accomplish something small than avoid tackling whatever you think you "should" read. So, with that said...
What shall I read?
First Step: Find your goal. What are you trying to accomplish? Your goal might be to learn something or be entertained. Both goals are awesome! Some studious types look down their noses at those who read "fantasy" or "fiction" as if its the real F-word! Other types (fiction readers) look down their noses at those who read "dusty" tomes, by "dead people" learning "impractical" things. Stop fighting, you two! Don't be ashamed at reading either genre! Both genres are needed, and both are connected.
If your goal is to meet a specific need (learn to combat my friend's attacks on my faith) then you should look for a specific book (I recommend "A Shot of Faith to the Head" by Mitch Stokes) but if your goal is broad–"I want to learn about apologetics" then, while the aforementioned book might not be bad, a more fitting book would be one that is also broad, such as "Reasonable Faith" by Bill Craig. Tailor your goals and the spectrum of specific/broad books to narrow your search.
Second Step: Find mentors. I mean by this that you should find an authority in whatever field you are looking in to help recommend the best book for you. The two best authorities, in my experience, are Web sites such as goodreads.com or whatshouldireadnext.com, and teachers in the field you are considering reading from.
For example, let's say you are looking for a good book on the Doctrine of Man (Anthropology) which is a sub-discipline within Theology (I understand its also a secular discipline, but I'm talking about theology here.)
Once you have your goal in mind (Let's say it's pretty broad, you just want to learn more doctrine, but want to focus on that particular part, which often precludes broader works such as a "Systematic Theology" which will introduce the reader to many theological topics but won't go very deep.) then you should consult your authorities. Find an authority within your theological stream (Protestant, Catholic, Evangelical, Lutheran, Baptist, etc) because while your authority might recommend books outside your stream, oftentimes the point of view is so vastly different (The view of man from a protestant or catholic viewpoint is going to be very different) it's good to paddle in your own stream.
Let's say you are reformed, and so your reformed authority (who knows your goals) recommends "The Christian View of Man" by Gresham Machen, and "Created in God's Image" By Anthony Hoekema. Both suit your goals and both are within your theological stream.
Summary: It's better to read something easy than NOT read something that is hard. The first step is to find your reading goal–whether it's to learn something, be entertained, respond to a question, research an interest, etc. figure out how broad or specific you want to go. The second step is to find an authority to help recommend a book to meet your goals. This can be either crowdsourced (using websites such as goodreads) or submitted to an expert in the field you are looking into. Try to find an expert in the stream you're paddling in. If your a flat-earther, look to experts who might also be flat-earthers. Sometimes its good to wander outside your stream, but only if you have a big enough boat (ie are discerning enough to handle differing views in that field).
Also, feel free to reach out to me for any book recommendations! If I don't know of a good book I usually know someone or something that CAN find you a good book. My email is firstname.lastname@example.org and I'm on twitter @philomathical