The most important step in preparing for battle is choosing whom to take with you. You can choose only a set number of units to take into battle. Some chapters require you to take certain units. At least one of the main characters (Eliwood, Hector, or Lyn) are required in every chapter.

When picking units, it's important to understand the battle objectives, as well as your enemy and the terrain of the battlefield. You may choose Mages and Archers for long-range attacks, or Paladins and Peg Knights to cover a lot of ground quickly. You may want a Thief to pilfer items, and a Troubadour or a Cleric to heal other units. If your enemy uses a lot of lances, you'll want a Warrior or Berserker to counter with their axes. Plan your attack carefully, and be mindful of your units and their statistics.