Take courses that will develop your communication skills, reading comprehension skills, logical reasoning, and analytical skills. (There is no pre-law curriculum other than taking a wide array of liberal arts courses.) Law schools seek diversity in majors.
Pick a major you will enjoy. If you are in a math or science major, seek out writing opportunities and writing-intensive courses so you can develop writing as a skill. Do not pick a major because you think it will increase your chances of acceptance at a law school.
Seek leadership positions in selected student organizations.