The "Major" Question
There is no required major for law schools. Law schools accept majors from all majors. Find a major you like and excel in it. Grade point average is such a strong determining factor in the admissions process you want to major in something you will succeed in. What counts is the intensity and depth of your undergraduate program and your capacity to perform well at an academically rigorous level.
What courses to take?
There is no prerequisite coursework for law school. Plan on taking courses which challenge you and develop strong skills in writing, reading comprehension, analytical reasoning, systematic problem solving, and oral presentation and/or debate.
Grade Point Average (GPA)
GPA is one of the most important determining factors in applying to law school. Law schools will review your overall cumulative GPA from all undergraduate institutions you have attended and will also calculate a yearly GPA. All courses completed at the college level will be calculated into the GPA, not just those taken within the major.
If your GPA is not as high as you would like it to be, all is not lost. Demonstrating continued academic success will help you in the admissions process. Improvement over time reflects your ability to work hard and also grasp increasingly difficult material throughout your college career.
Be selective when using the S/U option and whenever possible choose courses that engage your interests and take them for letter grades.
The LSDAS converts "U" to an "F" and calculates it into your GPA as a zero.
An "S" is given no value and is not factored into the GPA.