I usually just watch initially how comfortable the kids are with each other, and how comfortable the visitor is with being in an unfamiliar home. If they're OK with each other, they're likely to just "take off" and go on their own. If there's hesitancy, I usually start by having my daughter give a tour of the house, making sure to show the significant rooms like play room, bedroom, and bathroom, and if any rooms are off limits. Also, if you have any rules-like no TV- make sure you tell the friend that from the start. Pets can also be a great ice-breaker. If, after a tour of all the fun places, they're still having a hard time, then introduce your craft. Plan for there to be a snack/drink break, too. Some playdates go smoother than others. Try to let them find their own things to do. Kids at this age usually like to explore their friends stash of toys, to check out what they haven't got. Good luck, and have fun!