If you don't have cherries from the tree in the yard and you buy them from the market, be sure to choose slightly larger ones, not too small. The small ones are also good for sour cherry wine, but for the freezer I recommend "fuller" cherries.
So that, after removing the pits, there's more than just the skin.
Wash well a few times and let drain.
By the way, if you notice any worms, don't rush to throw them - keep in salted water for 1-2 hours and then rinse several times.