If you're renting a truck, try to get one with unlimited mileage. While it's a bit more expensive than one with a set number of miles, you can save a lot of money if you end up driving more than you expect. Having unlimited miles can be useful even if you're moving a short distance.
Try to avoid returning your moving rental late, if at all possible. The late fees tend to be very expensive, and may make you wonder why you bothered moving yourself at all. It's best to rent for at least a few hours longer than you think you'll need the rental.