If you're appreciating volunteers, I assume you're both thankful for their efforts and trying in some ways to keep them motivated and coming back. There's one mistake that hurts your group on both of those counts: leaving out volunteers or being somehow exclusive with your thanks.
Do you only appreciate those who've given a certain number of hours or volunteered at a certain senior level? Do you have tiers of appreciation, like a luncheon for some and a note for others? Both of those habits are surefire ways to get branded with a clique reputation. It's not unfair to appreciate stalwart volunteers more than dabblers, but it sure is counter-productive.
My advice: Thank everyone well and equally. If in doubt—thank. It's far better to thank 14 people who didn't do much of anything than to leave out one volunteer who did help.
Ensuring that your volunteers feel valued is the best way to keep them coming back. And it isn't hard to do. Here are some resources that can help:
Originally posted in 2015 and updated regularly