After escaping the failed attack on King Garon in Cyrkensia, Camilla launches an assault against you in Cheve.
Preparations Before the Battle
A great many of the enemies south of the river have weapons that are effective against lances and hidden weapons. But north of the river, it's a different story. Many of the enemies up there have weapons that are effective against swords and magic. There are also quite a few enemies around the battlefield that have weapons effective against flying units.
Rout the Enemy
Get rid of the Outlaws quickly so you can steal the 3000 G that each one is carrying, and prevent them from killing your flying units, and prevent them from capturing the villages.
If you visit the villages, you will get a Heart Seal, Spirit Dust, Talisman, Wane Festal, Steel Yumi, and 10000 G.
There are Dragon Veins around the battlefield. Activating one will cause lightning to hit a particular area. Any units in that area will have their HP reduced to 1.
Be aware that there is one such Dragon Vein near Camilla. It will hit south of the western bridge, so don't use that bridge or Camilla will hit your units as they try to cross.
If you enter Camilla's attack range, she will come to you, so be careful if you are close to the river but aren't ready to fight Camilla.
Hans is an especially difficult opponent, but using a Dragon Vein will make him much easier to get rid of, so do that if possible.