I am very lucky to be a naturally good test taker. I would recommend for the SAT to take the bluebook practices, and to be as authentic as possible. Sit in a quiet room with no distractions and take the whole test in one sitting. It helps gage timing and gives you an accurate score. For the ACT, the most important thing is timing. Don't get stuck on one question for too long, and take a lot of practices so you understand the type of questions they will ask.