Before you begin to prune oleander, make sure you wear gloves and protective clothing. All the parts of this plant are highly poisonous to both human and animals.
Oleander is an easy plant to prune. It should be done in September or at the beginning of October.
Start by cutting the plant just above the leaf node. This is the area where three of the leaves come out from the branch. New branching will come from this cut. Do this all around the plant.
Pruning will help produce more branches that give more flower clusters. Don't be afraid to cut them back if they need it.