I have struggled on whether to go Law School for the past two years and I can still honestly say that I don't know. I have read books and I have talked to lawyers, professors and career counselors.
Major doesn't really matter too much, but it would be got to take philosophy and rhetoric courses (as others have mentioned) to help the critical thinking aspect of things.
If you plan to apply to Law School right out of undergrad, GPA is very important. Don't take easy courses just to boost up your GPA, the admissions people look at your course work and your school in putting your GPA in perspective. The LSAT is just as important, make sure to prepare for it because it very well could determine where you'll be able to go.
Going to a top tier school is exponentially better than going to a 3rd-tier school. It has been mentioned, but there are firms that will only consider candidates from the tops schools. In that sense, a 3rd-tier school will limit your possibilities of employment and your salary base/ceiling post graduation.
Don't feel like you have to go to Law School straight out of undergrad. Take a few years off and get into the work force. Not only will you be able to reevaluate whether you really do want to follow this route, but you will also gain valuable work experience that does make an impact on how Law Schools look at you. Furthermore, working for a few years, will lower the impact of your GPA a bit -- of course, the LSAT will still be as important.
Law Schools is very expensive and time consuming so don't rush making a decision.
I recommend looking/buying at the following book:
How to Get Into Law School
It is a great read, it is very informative and it will really make you think about your decision. Being in a similar situation as you, this is the best advice I can give you, if you have any questions for me feel free to PM me.