The hardest part to harvesting wild cherry bark is finding a tree. It's hard to identify trees in the winter, so if you don't know where one is, wait until summer and keep your eyes peeled. Chokecherry trees are similar to wild cherry, but wild cherry is a big large tree and chokecherries are more akin to shrubs. I found several large wild cherry trees last summer and noted the location so I could find them in early spring/late winter.
If you think you've found a wild cherry but aren't sure, break off a live twig (one that stretches and peels; a branch that snaps off is dead) and sniff it. It will smell like cherry. My tree smelled like cherry with a hint of tomato.
Pick a young branch or two and cut off with pruning shears. Bring them in the house.
After you've come inside, you can cut off the budded ends of the branches. I put my ends in a vase with some sugar water. Maybe they'll grow some leaves or flowers for me!
Scrape off the green bark with your knife.
You can use the green bark fresh, or you can use it dried (but DON'T get it too hot!). I am going to dry mine and use it in a cough wine. Wine or tincture is a great way to use this herb because heat destroys the medicinal qualities.