One possible version:

　　Dear David,

　　Glad to receive your e-mail. Our school has made safety rules for us to follow. Let me tell you something aboutthem .

　　We are asked to be careful with electricity when we are using it. It is dangerous to play with fire, for it may cause terrible accidents. We should make sure doors and windows are shut before we leave.Besides, we are not allowed to swim alone, especially in deep rivers or lakes. If we really want to, we must go to the swimming pool with our parents or teachers .What‟s more, following traffic rules is also very important. Everyone should watch out when crossing the road. And our school warns us not to play on the road.

　　I think these rules are necessary as safety comes first. Have a good summer holiday!

　　Yours, Wang Wei