Tag in all your weaker partners first, then tag in your strongest last. Do not forget to heal them to get the experience. Then, finish with the strongest Digimon. All the digimon will get the same amount of experience.

Note: This trick requires a controller with a auto-fire feature. Go anywhere where you can kill the enemies in one hit with attack. Set the auto-fire to X and use a rubber band to keep X and the D-pad held. Allow the game to remain in this condition for an extended amount of time.

Go to Amateratsu Dungeon. Fight until you reach the Fire Dungeon. Defeat the leader there and he will give you an EXP Adaptor. This item can get you more experience in battle for one Digimon.

Get to the north sector in the Atmurutsu server, or to the north sector.