Write it all down. Download the "Babysitter Cheat Sheet" -- with space for emergency numbers, where to find a flashlight if the power goes out, special feeding or allergy instructions, and more -- from SitterCity.com. Fill it out and post it by the phone.
Give a house tour. Walk your sitter through your digs, showing her where things are (extra formula, bibs, fire extinguishers) and how to use them.
Share some secrets. Clue him in to your baby's favorite blankets or lullabies, her tendency to unroll all the toilet paper if you don't shut the bathroom door, and the creaky floorboard that wakes her up.
Do your homework. Bathe and dress your baby for bed, so your sitter only has to change his diaper; mix and premeasure bottles; and administer medicine yourself. Now, go have some fun!