My rental golden rules: Book early at the current prices you can find, re-book often when finding a better deal (making sure to cancel the previous reservation(s) made), follow the Transportation Forum and the thread for the month travelling to see deals, codes, etc others have found or are using for the same period, watch to make sure comparing apples to apples in an all-in cost when comparing rates (Dollar an example where they put up front the base rate and you do not see the total rental cost till completing the booking), and only do a pre-pay if you are sure or comfortable the rate will not drop lower than (or are willing to stop looking to not know such).