Rule Number 1 - HAVE A CONTRACT
 
Freelance Photographer/Videographer Client Contract
 
Regardless of the scope of work, relationship with the client or $ fee, always complete a contract between yourself and the client. This will ensure you're covered in the event of changes, disputes or cancellation. This will also give the client peace of mind and a place to track changes. You'll also look professional. 
 
I also like to soften the language - "Photography Agreement" sounds less formal than "Client Contract"
 
17 Legal Clauses