Read more slowly and more carefully. If you're taking timed diagnostics or timing each section, try doing it without looking at the time and see if that makes a difference. Go back and re read questions, and read all the answer choices...even if you think the answer is "B," go down and read all of them. I know that it sounds like pretty basic stuff but its easy to get overwhelmed. Once you actually take time to eliminate the silly mistakes, you'll be able to recognize the right answers more easily and be able to speed up again.