You could use this as a fundraising copywriting checklist: This post at the Hilborn Blog, Twenty things you should know before planning your next direct response campaign includes a very handy list: Components of a great letter.
- Make your appeal letter optically pleasing and inviting to read.
- Write small paragraphs and short sentences. Make use of image.
- Be conversational and informal.
- Feature an emotional story that personalizes your organization or cause.
- Thank your donor. Then thank them again.
- Recap what the last donation accomplished. Explain what the next donation will achieve.
- Attribute organizational achievements to donor support.
- Try to relate monthly giving and donation levels to an outcome.
- Ask for support up front, in the middle and at the end of your letter.
- Don’t forget the P.S., support the ask!
I'd add one item to this list:
- Have a clear, specific, understandable, compelling call to action. Make sure the donor knows exactly what you want her to do. And it should be something she already wants to do anyway.