2 things:

1.) Specify a cause and/or foundation in advance.  Make it extremely clear *who* the coins are going to, from the name and contact info of the org all the way down to the payment address.

2.) Full disclosure.  Release your real names and contact information.  If possible, register a charity specifically for this.

If you do those two things, your coin will succeed where all previous "charity" coins have failed.  If not, you're probably just another scammer.