Answer The Phone!
While you are busy getting camp ready for the summer and greeting the first group of happy campers, who's in your office answering the phone?
First of all, make sure someone is -- nothing frustrates parents more than not being able to reach a live human being at the place where their child is spending his summer.
And make sure that person is friendly, knowledgeable and helpful.
Here is a great blog on the subject from camp director Byron Hill: http://networkedblogs.com/iPFwu