I often see high school students asking similar questions about law school, so I thought I'd post some generalized advice that covers the main questions high school students ask:
1) What should I be doing now?
Ask family and friends in the legal profession what their jobs and lives are like so you can make an informed decision as to whether this is the career path for you. Otherwise, you need do nothing you're not already supposed to be doing. Develop your writing and critical thinking skills and focus on getting into a good college. Stay out of trouble. The state bar association will conduct a character and fitness review on you during or after law school and you will be required to disclose your traffic and criminal record and any instances of academic misconduct in college. While a few youthful indiscretions here and there are unlikely to keep you out of the profession if properly disclosed, it's best to have as clean a record as possible. Otherwise, have fun and enjoy life.
2) Are there any classes I should be taking or any extracurriculars on which I should focus?
No. Not only do law schools have no interest in your high school activities, listing them on a law school application might hurt you if it looks like you're living in the past and haven't achieved anything since high school. Likewise, law schools and legal employers will have no interest in any classes you took in high school. Unless you did something extremely remarkable or very rare in high school (like start a successful corporation or get elected to a local political office), don't put too much stock in your high school achievements. The upside of this is that if you had a lackluster high school career, you'll have a second chance in college to achieve the academic success you may have missed out on in high school. Your high school GPA, SAT, and ACT scores don't matter and you have a clean slate starting college. As a sidenote, the type of high school you attend is not relevant. I got into a top 14 law school and that was the first private educational institution I had ever attended - my classmates whose parents shelled out tens of thousands of dollars on prestigious private boarding schools had no advantage over me.
3) What colleges are the best to attend if you want to go to law school?
The best one you can get into/want to go to. Far and away the biggest factors in determining your law school admission opportunities are your college GPA and LSAT score, factors over which you have no control right now. There is some marginal benefit attached to having gone to a prestigious university, but it isn't so great that it's worth going to a school you know you'll hate for the sake of gaming the law school admissions process.
4) What college major should I select?
Whatever you want. There aren't really any majors that give you a noticeable advantage in the law school application process. People like to recommend political science and history. Don't major in these subjects unless you enjoy them - they don't confer any meaningful advantage in law school. The only undergraduate majors that can affect your law career substantially are those in engineering or the natural sciences because they may qualify you to take the Patent Bar which in turn can allow you to prosecute patents before the US Patent Office. Unless you're really interested in patent law, there's no pressing need to worry about this.
5) Are there any books I could read that would give me a leg up in future law school admission?
Not really. You have no way of knowing how any law books you read now will gel with the curriculum at your future law school or the preferences of its professors. You will also probably have forgotten any law you read in high school by the time you get into law school. There are plenty of books that describe how law school works (Law School Confidential by Robert Miller seems particularly popular) for prospective law students that could give you a sense as to whether law school and a career in the legal profession are right for you. However, these are generally written for college students, and they could be out of date by the time you actually seriously begin the law school application process. While there's no harm in reading them, it won't give you any sort of competitive edge to do so now. It's also too early to study for the LSAT. At most law schools, your LSAT score has to be from within three to five years of your admission. There's no advantage to taking it any earlier than you have to, and no advantage to studying for it years before you take it. You probably have enough on your plate now - don't worry about this.
Lastly, I would add that you have plenty of time to decide whether law school is what you really want to do. Law school involves an enormous commitment of time, effort, and money, and the profession is not as glamorous or lucrative for most people as they think. The decision to go to law school should not be a hasty one. Don't plan your life at this point around future law school admission possibilities. Remember that life is what happens to you when you're making other plans.