If you can write on the thing you are reading, try underlining or highlighting key ideas: dates, names, important facts. If you can't write on it, write down those key ideas. Don't write down EVERYTHING, just the most important parts.
When studying, if there are specific things to memorize (Raleigh is the capital of NC, Pearl Harbor was bombed on June 7), try using flash cards. Get a stack of index cards, put the question on one side and the answer on the other. When you can go through the card three times without any mistakes, you really know the material. You can also use quizlet.com to make online flash cards to study.