Sweet cherries need to be thinned out after the harvest. Clean cuts heal very well at this time. Remove all sick and weak branches. If some branches still carry some fruit, you should take these off as well. They could cause fungal diseases such as brown rot. Moreover, if some branches are too close to another, you should either remove one branch or try to divert the branches. Using a bast rope, you can try to direct the branch in a different direction.
Sour cherries like morello cherries also need to be pruned. To do this, remove shoots which have brought fruit at the next branching. Keep shoots which grow in an upright position – they will most probably carry fruits in the next season.