This article is from the Recreational Figure Skating FAQ, by Karen Bryden with numerous contributions by others.
There are no well defined rules on tipping your coach. A few people
tip their coaches on a regular basis, many do not. You can express
your appreciation in a perfectly appropriate manner by giving your
coach a small present on their birthday or for Christmas. Ideas for
presents include (but are not limited to) gift certificates,
subscriptions to skating magazines, tickets for a coming ice show, a
bottle of fine wine, etc.