Always try to have at least one other person working with you. 

Check your cell phone's strength and signal prior to starting the open house. 

Upon entering a house for the first time, check all rooms and determine several escape routes. 

Make sure if you escape through the back door that you can escape the back yard.

Always walk behind a client. Keep yourself bewteen the client and the escape route.

Have all visitors sign in. 

Communicate often with someone to "check in". 

Check all the rooms after the open house. Never assume everyone has left the premises.