You have to do a “pre-law” major to get into law school (Political Science, English, History etc)
In undergraduate education, or even any graduate education pursued before law school application, the areas you explore are entirely up to you. So long as you demonstrate good work ethic and the ability to analyze, research, and think critically, there is no specific field of study you must major or minor in.
You have to intern in the legal or political field
Law school admissions want to see who you are and what you're interested in. Internships help build your resume, make money if paid, and explore potential occupations. They do not have to be related to law or politics; they must simply be something you want to put time and work into.
You have to be involved with law related activities on campus
While law related activities can allow you to network and engage in mock trials or MUN, don't join out of a sense of obligation. Join because you want to spend your free time in those spaces. If you're not genuinely interested in an activity, your contribution won't be as great as it could be with something you're passionate about.
You have to do paid internships
Paid internships help pay for undergrad, save for law school, and network with potential employers. However, don't turn down an internship simply because of lack of pay. They're great for providing experience and can still serve as potential future employers and networking opportunities.
You have to attend straight out of undergrad
I was shocked to learn that, at my college, only about two students apply to law school their senior year. This is not to say that only two Bryn Mawr alumni per year attend law school. Rather, most graduates take a gap year before applying. Your letters of recommendation, LSAT scores, and essays are good for 5 years in the LSAC's "common app." On a depressing note, once you graduate law school you make have to work for a very long time before you can get time off. In this sense, gap years provide a sense of relief before diving back into academia. Some individuals pursue graduate school before applying for a JD to further bulk up their resume or pursue another passion. There is nothing shameful about taking a gap year nor will it affect your ability to attend a prestigious law school, if that's a goal of yours, or become successful in the professional realm.
All in all, being pre-law and wanting to attend law school doesn't mean you have to do anything other than apply to and attend law school!