Decide upon a specific time to read your chosen book. It's best to plan for shorter sections of time instead of a large block so you'll have time to process what you've read in between sessions. Pick a time of day to read when your mind is working at its best, whether that's in the morning or the evening.
Read through the whole book once to get the basic idea or basic story. The point of the first reading is to get an overview and to avoid being stuck on details. If you come across anything that's difficult or confusing, mark the page with a note. If the book is yours, write directly on the page.
Read through the book again to find the sections you marked the first time. Reread anything that you didn't understand before and try to relate it to the rest of the book. If needed, use a dictionary to help you comprehend complex words or concepts. As you read, think about what the book is saying or arguing. Look for information about the author or organization that would give context. The acknowledgments, introduction and biographical statement may be helpful in this step.
Talk to others about the book. This will not only reinforce what you just read in your mind, it will help you to form an opinion about it. Put the ideas into your own words and make a decision about what you think about them. It may help to talk to other people who have read the same book who can perhaps offer a different perspective.