You only have limited time and energy. You can be selective by getting into the habit of previewing a book . Try to immediately establish if the book will be useful. If you think the publication will be useful, skim through the introduction to get an idea of the contents. You are now in a position to decide whether to read the whole chapter.
Some students worry about how fast or slow they read.
Your reading speed will improve with practice. You could, for example, read a newspaper such as the Guardian or Independent for 15 minutes a day and you will soon begin to see improvement in your reading. You need to find a balance between reading and understanding. It is important to be able to read quickly, but you also need to maintain understanding. Sometimes you need to read something a few times before you begin to understand it.