Obviously compare rates from the major players: budget, avis, hertz and make sure to compare the total price (including taxes and surcharge).
Inquire about any special offers and membership discounts. AAA usually offers discounts, but you can also find plenty of coupons on the web.
Also, if you have AAA, or auto insurance, the coverage might cover rental cars so you can waive additional insurance from the rental car. Make sure you know what your policy states.
Was wondering if any knows if is it cheaper to book online or in the store? I am guessing online.