To make sure you have understood a text, ask and answer questions. Websites such as Reading Comprehension offer worksheets that you can use. The material ranges from essays to poems, and the structure is one or two sentences followed by multiple choice questions. The material on this site is intended for teenagers, but once you have mastered the technique, you can apply it to any text you read. The trick is to ask questions paragraph by paragraph, so that your memory is formed in small pieces, rather than trying to absorb the entire text at once. Doing the latter may cause you to forget essential details, and you might miss the nuances and allusions in the text.
When you are studying for an exam, you may need to get through a large amount of information in a short period of time. Educational texts are not written like commercial or entertainment books. Usually, the first sentence in a paragraph introduces the information, and the last one summarizes it. Read the first and last sentence in each paragraph, then read all the subheadings in the section. It provides a good overview of essential content. Once the basics are in your mind, you can then read the rest of the paragraph and fill in the framework material. Should you find a question on the topic, your mind will remember the headings and summaries, and you can then fill in the required details. To test your skills, skim a passage, then answer comprehension questions. See how many you can answer correctly without referring to the passage.
You can test your reading speed at www.speedreading.com. You should aim to read 300 words a minute and understand about 75 percent of the information you have read. Answer the comprehension questions to gauge how much you have understood. You can improve your speed by reading frequently. Whenever you want to read, select a portion of your text and put it into a speed reading test window such as Spreeder or Eyercize.
Move your eyes gently from one word to another while you read, and try not to go over what you have already read, as doing so slows you down. Sometimes, when you are trying to read quickly, you will jerk your eyes over the words, and you will not understand what you have read. Avoid jerky motions, and instead move your eyes in a relaxed manner.