Doing well on the science exam opens doors for you. Be one of the people that make humanity understand the world better. As someone working in the science field, others look to you for solutions. This starts with effectively studying for the science exam.
Start studying for your science exam before the course. Obtain your science textbooks before the course and read them completely. Read all the chapters. Go back and read the first two chapters twice. Once to reinforce your earlier reading, a second time to focus on highlighting efforts. Base your highlighting on the learning objectives.
Write notes in every science class you take. Review every note you take until the night before the exam.
Take every science lab you do seriously. A science lab project gets you into the scientific mindset. You want to be in this mindset before the exam. Do your science labs like your life depend on it--even though it's a classroom controlled lab. Hands on knowledge of the scientific process makes science exam taking easy.
Get together with your friends taking the same science class and form a study group. This group can also include other students taking another science class under the same instructor. Assign a series of chapters per person; quiz each other based on these chapters. Use your study group as an oral practice run for your science exam.
Study your text in areas where you're not comfortable with the learning objectives. Understand that the learning objectives hint at the science exam questions. Get a full nights rest the day before the exam. Refuse breakfast buffet invitation if your science exam is in the morning. Apply this same principle if your science exam falls in the afternoon or evening.
Read your entire exam before taking it. Let your subconscious mind work on the exam while your conscious mind grapples one question at a time.