Choose a hatchery near you, if that's an option.
Choose a hatchery that has the breeds you want, and has them all available when you want to receive them.
Choose a hatchery that has good reviews. You will have to do some research on this issue.
Do a price comparison, taking shipping rates into account.
Never order chicks to arrive during a mail holiday week. Schedule them for shipping at the beginning of the week.
Contact your local post office, give them a heads up about expected arrival date. Be sure your post master has your phone # and address, and knows to hold chicks, and call you immediately upon arrival, even if it's in the middle of the night.
Have your brooder set up ahead of time. Be sure you have Poultry Nutri Drench on hand, and use it for the first 2 weeks. Make sure your chick starter is fresh. Check out MHP brooding system, brood chicks in your coop if that's at all possible.