Decide what you need the truck for and plan accordingly. If your child is moving out of the house into his first home, he may not have too much stuff and a small truck is all you need. If you are moving across the country, then you will need a much larger truck.
Plan on whether you will move yourself or have someone move you. Before you call to rent a truck, you need to know all the ins and outs. Make sure everyone is on the same page before you rent a truck. Renting a truck can include the movers actually moving the stuff.
Call different truck rental companies to see who has the best deal. Make a list of your requirements and get an estimate on the truck you need to rent. Don't commit yourself at this time until you have gotten estimates from a few different companies.
Write down all the information you have gotten from the various companies and talk it over with whoever else has to make this decision with you. Decide on the truck you want and rent it.