Non-profits of all sizes, you need to be THANKING your donors for their gifts.
Not just the obviously automated e-mail that your donation platform sends out, but an actual paper in the snail mail meaningful thank you letter. Here's the clear message you're sending when you don't thank your donors... "Your gift was so insignificant to us that we can't even be bothered to meaningfully acknowledge it, but we did cash the check."
Yep, it'll cost you a little bit of money and a little bit of time, but, you need to be doing it. That's just the cost of doing business.
This is actually an area where smaller orgs. have a huge advantage over large non-profits. These larger non-profits are often slow moving machines and can't get thank you letters out the door quick enough for them to be meaningful. Smaller non-profits are able to move quickly and 'thank before you bank', which makes your donor feel like you really care!
Thank you for coming to my free class, don't forget I'm available for hire.