People who prep for the SAT have much higher scores than those who don't. Thinking of applying to an Ivy League School? Don't bother unless you are in the mid 1400's. State schools want 1200 minimum with a high GPA. You could chance it and take the test uncoached or you could make sure you maximize your super score.
Improving your score is simple:
1. Work on skills that keep showing up on recent SAT Tests
2. Become comfortable with the format of the test.
3. Learn how to manage time and emotions during the test.
4. Work with someone who is an expert in the subject they are teaching.