The first thing is to stop the bleeding. Put a cold compress over the area from were the tooth was knocked out. This will help prevent bleeding. Lie down with head back so that the blood drains away from the socket.
The next thing is to preserve the tooth that has been knocked out. In order to ensure safety of avulsed tooth, put it in a clean sandwich bag and place the bag in ice container. Keeping the tooth in cold will maitain its vitality and it can be successfully placed back in the mouth. Take care not to touch the root area of the avulsed tooth as it can damage the area.
Also you can get ready-made tooth preservative by the name "Save a Tooth" from the pharmacy. It already contains the mixture into which you can preserve the tooth. For more and detailed info you can visit the link...http://www.identalhub.com/dental-broken-or-knocked-out-baby-tooth-924.aspx