DON'T insist or be challenging in the way you come across. I had to bite back my overwhelming urge to tell him to send it to Disney if it was so Disneyesque. We had our own style, thank you very much. DO be creative, but don't overwhelm me with tokens to remind you that we have your project. As sweet as that was, it just made it worse for me when we passed on her project.
Assertiveness can impress but the line is hairline-thin before it becomes aggressiveness.
DO reference your phone conversation if you are asked to send in a query or script. Include a post-it or small note directly to the assistant that was kind to you on the phone. Include in the letter addressed to the development exec how polite and gracious the assistant was. If you talked to the development exec themselves, remind them and thank them for the time they took with you. DON'T leave a voice mail message if you are calling to query.