In my opinion, if you know you want to be a lawyer, I would recommend going straight to law school. A masters degree isn't necessary and unless you are planning on being a lawyer in a very specialized field (such as patent law) a masters degree isn't going to be all that helpful in helping you secure a job. If you really want a masters degree as well as a law degree, some schools will allow you to do joint degrees (the most common of which is a JD/MBA), which is great because some classes can be used for both degrees so you can generally get both degrees more quickly than the time it would take to get one degree after the other.
If you aren't sure that you want to be a lawyer, I think that getting some real world experience would be more helpful than getting a masters degree before law school. Getting out into the real world for a while can be a great experience and help push you out of your comfort zone to decide what you really want to do with your life.