Here's a helpful post from Frogloop: Six Online Fundraising Appeal Goofs to Avoid:
- The first call to donate money with a hyperlink is buried five or six paragraphs in the fundraising appeal.
- Underlining sentences that have a call to action with no hyperlinks to donate.
- Hyperlinks don't work.
- Not including a donate link in a fundraising message re-forwarded to your online donors as a reminder.
- Sending several fundraising appeals over the course of a week.
- Putting the world's weight on your donor's shoulders with large and unattainable goals.
I'm not so sure about #5. I've seen a number of cases where emailing several appeals on a very quick cadence works quite well. It's probably something for further testing and research.