It is good beekeeping practice and swarm prevention to have young queens in your colonies. A young laying queen produces maximum pheromones that discourage the bees from building queen cells. Give her plenty of space in the brood nest. If the bees haven't built queen cells, the following techniques will reduce the likelihood of swarming; but won’t eliminate it.
1) Add an additional super before the bees become overcrowded while ensuring they can occupy the added space comfortably. Don’t pile on empty supers for the sake of it.
2) Create a pyramid structure of brood. Lift up 2 to 4 frames of brood up from the brood nest into the super above, push the remaining brood frames together and add empty frames in the space. Brood arranged in this pattern requires more nurse bees to cover and care for it forcing them to spread out reliving congestion in the brood nest. From my experience, this method is the most successful and easiest to implement. As the brood hatches, cycle empty frames around.
3) Find and isolate the queen. Remove 3 or 4 frames of bees and brood containing eggs, grubs and sealed brood to form a nucleus. Shake 2 additional frames of bees in as the flying bees will return to their original home. Site next to the main colony. Return the queen to the parent hive pushing the remaining brood frames together and adding empty frames into the space. When the swarm season finishes and the new queen in the nucleus is laying, requeen the parent hive by kill the old queen and united the two colonies together using the newspaper method.
4) For very strong colonies, physically split them in half. Move one of the boxes to another location while the other remains in its original location with a super added. Ensure both colonies have eggs, grubs and sealed brood so the queenless one can raise a new queen. This technique will increase your colony numbers without losing swarms.