How many of your new donors have given their second gift?
That's an important question, because it's fair to say a donor isn't really a donor until they've given twice or more.
To motivate that critical second gift (and every other gift), the best thing is to make the donor feel good about what they've done. Make the donor feel like a hero. The hero, as posted on the Communicate! Blog at My Hero!
For your donor to renew, she or he has to feel like the hero of the story. You are the one who is going to make donors feel like heroes. And the fundraising appeal letter is just one of the many times during the year you have an opportunity to do that -- but it's a crucial time.
If you thank donors by saying something like, We took your donation and did some wonderful things with it because we are a superb organization -- that doesn't make them feel like a hero. At best, it makes them feel like a hero's sidekick.
Give the donor the credit for making great things happen.
Then they just might keep on giving!