I don't know that you will actually be able to put money aside while in law school. I think the focus will be on minimizing what it costs you to live. However, you don't want to "waste" a lot of time on handling your finances, as you will need this time for academic activity.
A lot depends on your living arrangements. If you will have a kitchen, you will want quick, easy, nourishing, and inexpensive meals. It's important to keep your brain properly nourished! Being single, I tend to cook a big batch of something that will last 3 days or so. Casseroles, crockpot meals, etc. If the school offers a meal plan that is reasonably priced, go with it! While at school, carry snacks and water with you. Avoid vending machines!
Shop around for textbooks. Also, take advantage of anything included for "free" with your tuition. For example, if you can print for free at school, do it! Also get the best cell phone and internet plans that you can. There are many student discounts - sometimes you have to ask!
Clothing: There are lots of good deals at second hand stores. Seriously. However, make sure to get a good pair of shoes. This is important if you are doing a lot of walking!
Transportation: Bicycle? Bus? Do you have to have a car? Again, a lot depends. Where will you be working? How will you get back and forth? If the only reason you need a car is to work, evaluate whether the job is only paying the cost of maintaining the car. If so, skip the job, skip the car! Gives you 15 hours more free time!
Entertainment: Again, look for discounts. Check out the student performances.
Learn to distinguish between "Wants" and "needs." You need transportation. You want a sports car. The more frugal you can be, the more you can save!
If you truly want to put money away, the only way to do it is to "pay yourself first." That means, every week/month/paycheck you take $20 or so, and put it away, before you even begin to pay bills or buy groceries. A strict financial discipline approach will allow you to do that!