Five jobs in a battle line
A battle line is a set of jobs. Infantry holds or fights. Missile troops shoot while the lane stays clear. Cavalry charges and comes back. A monster uses its mass in a gap. Artillery fires from behind the troops that keep the enemy off the crew.
Creative Assembly describes the battle as soldiers, monsters, heroes and magic, and points to an Empire mix of infantry, cavalry, artillery and magic as the way to learn those systems. Bretonnia is the cavalry-charge example in the same guide. The regiments below are samples of those jobs.
Kossars, Streltsi and Lothern Sea Guard can shoot and fight. Once a hybrid is stuck in melee it has stopped shooting. Count it as one job at a time.
The front line
The front receives the enemy and keeps them off the troops behind it. Empire Swordsmen, Dwarf Warriors and Jade Warriors are shielded or armoured examples. Skeleton Warriors establish an undead line while characters and mobile troops work around it. Chaos Warriors are the armoured mortal line, with shield, great-weapon and halberd entries that are separate regiments.
Update 9.0 notes an Anti-Infantry Bonus printed on the unit card. Balance notes name the large-target stat Bonus vs. Large. Jade Warriors with halberds and Chaos Warriors with halberds are the polearm entries for large enemies. Open the card in the battle for the current bonus.
A wide front of ordinary infantry is what gives the missiles and artillery time. Sending the whole front forward with a monster opens gaps the enemy walks through.
Missile troops and a clear shot
Missile troops need a lane. Kossars and Streltsi lose the shot when the enemy reaches them. Glade Guard and Horrors of Tzeentch want space in front. Irondrakes are short-range guns: Drakeguns for infantry, Trollhammer Torpedoes for large targets.
Place the shooters beside or behind an opening, not behind a solid wall of friendly troops. When your own infantry reaches the target, stop firing into that fight or pick another target.
Cavalry that leaves and returns
Cavalry is a charge, not a second infantry line. Knights of the Realm are Bretonnia's lance cavalry, and the new-player guide describes that race through heroic knights and cavalry charges. War Bear Riders add a mounted charge to a Kislev line. Skin Wolves are mobile monstrous troops for a large target. Send them in from a side that is not already packed with spears, then bring them back out.
A cavalry unit that stays in a long melee has stopped being the reserve.
Monsters need a line in front of them
A monster is a large body for a gap. It does not replace the regiment that holds the front. Ogre Bulls need room to charge. Minotaurs are monstrous assault infantry. Tree Kin hold an approach so Glade Guard can keep shooting. The Khemric Titan is a construct monster that fights and shoots. Morghast Harbingers are flying constructs aimed at armoured infantry. They arrive over the line. They are not the line.
Keep a holding regiment on the ground. If the monster charges through and the front goes with it, the artillery and missiles behind have nothing between them and the enemy.
Artillery behind the line
Artillery fires while something else keeps the enemy away. The Fire Rain Rocket Battery and the Helstorm Rocket Battery throw explosive rockets into infantry formations. That is the Anti-Infantry Bonus job on the card. The Ironblaster is a mobile cannon. Choose its lane before the Ogres charge.
Friendly troops in the landing area make the rockets dangerous to your own line. Change target or stop. Cavalry and flyers can cross the field to reach a crew, so keep a reserve that can intercept them.
One army, then the campaign
A first formation is a front, missiles or artillery with a lane, and one mobile piece for a flank: cavalry, a monster, or both. Add a caster when the race has one. The lord leads the army. A hero embeds in it. Recruit the role you are missing from the settlement chain, horde, ship or race pool that faction uses.
If the recruitment list is missing the regiment, check ownership before you redesign the formation. Katarin's first campaign practises hybrid infantry. Karl Franz's practises the Empire line of infantry, missiles and artillery.