To become a lawyer, what should I do after college to work up to becoming a lawyer.

Most students seeking to become a lawyer major in something like Political Science, Philosophy and Law, or Criminal Justice. After completing your four year degree, you will begin applying for law schools. Before you start applying, you will take an exam called the LSAT. Your scores will determine which law schools you would be qualified to seek acceptance in. After law school, you must pass the Bar Exam for the state that you would like to practice in.

Like all great questions the answer is not always simple. Mareo's comment explains very well the mandatory steps to apply and be admitted to law school which are 1) complete your undergraduate degree, and 2) take the LSAT's.  The way that I read your question though, you seem curious about what you might do to better prepare yourself for law school and ultimately becoming a lawyer.  This is where the question becomes a little more complicated.  

My advice would be first of all to spend some time exploring what you want to do as a lawyer. As you can imagine, we perform many different functions across many different fields and all of them contain some level of specialization. Whatever path you take, your role as a lawyer will be as a trusted advisor so I would advise you to ask yourself who do you want to help? Having an answer to that question will give you a good head start on what kind of law you might want to pursue and how to ultimately get there. If you are in a position to before you begin your LSAT and applications, perhaps seek out opportunities to work in a paralegal or legal assistant role. You will build your professional network, get valuable hands on experience and have the benefit of first-hand knowledge of what the profession looks like from the inside. If you're not in a position to take a job in the field I'd encourage you to speak with as many lawyers in your area of interest as you can. Don't be afraid to send a sincere email directly to an individual lawyer who is doing something you find interesting. We love being asked for our honest opinion! 

Other generalized things you can do to prepare are to read voraciously! Run a google search for interesting cases and find ones with the actual case citation (e.g. 123 U.S. 456).  Read the actual court's opinion rather than news summaries of the cases. You'll get used to the cadence and nuances that the judge uses as well as the structure for citing precedent.  As a bonus, some cases are seriously fascinating! Really, you couldn't make up some of the stories that people have brought before the courts.  

Also, learn to type...fast, without looking at your fingers. In most cases your law school finals will be the only thing that you are graded on all semester and they are strictly timed. In those kinds of environments you will be limited to how fast you can read and comprehend the questions, how quickly you can organize your thoughts and arguments, and how quickly you can get those thoughts down on paper. Don't let your fingers be the bottleneck. When you're studying you'll also spend less time taking notes and get more rest which is also a huge advantage.  

Hope that helps. Good luck!