Prune lilacs after they have stopped blooming, when bees are no longer interested in the bush. To prune, start with trimming larger stems from the bush's center. This allows new shoots to develop on the outside of the plant, and creates better ventilation in the center of the plant. However, leave a rounded top on the plant. Get rid of any shoots at or near the ground, and cut off any unattractive or unhealthy branches from the main stalk.
Wait for a windy or rainy day to prune, if you must do it before the blossoms die. Although you are pruning in inclement weather, you will not have to worry about the bees bothering you. Prune as directed.
Spray the bush with a hose, simulating rain and chasing the bees away. Prune as directed.
Place a Bounce dryer sheet under or on top of a small bush--bees do not care for the odor and should vacate the area, allowing you some time to prune the bush as directed.
Dress in long sleeves, pants, gloves and a hat before attempting to prune a bush swarming with bees. Bees do not attack unless they feel threatened, and it is probable that you can work around them without getting stung.
Prune the bush as directed in the early morning or dusk when bees are not as active.