Typically viburnum shrubs need relatively little pruning. However to maintain shape an occasional pruning is required.
Although light pruning can be done at any time, the best time is immediately after blooming. For severe pruning or shaping, it is done best in late winter or very early spring.
How to Prune Viburnum:
Young shrubs can be pinched back to help maintain shape. Choose an upright stem and prune back to a node.
A node is where there is branching from the main stem. After pruning back to the node, than prune side shoots.
Do this pruning annually. Viburnums can withstand heavy pruning without causing harm, however do not cut back more than 1/3 of the plant.
Always prune any dead or diseased branching immediately. Be sure to clean your pruners afterwards with rubbing alcohol.