Put more troops per army
Why: more troops = more fuel = you take hits and strike for longer. All the sources:
What helps directly
Upgrades
Increase the number of troops per dragon
In Upgrades, raise "Dragon Army": each dragon carries more troops.
WhereStronghold › Dragon Care
Level
Grow the army by raising the dragon's level
Raise the dragon's level: its maximum army size increases (gained in combat or with meat).
WhereCombat / meat
Stars (relics)
Grow the army by raising its stars
Each star also increases the dragon's army size (and it's permanent).
WhereDragon relics
Related bonuses (good to know)
Upgrades
Reform your troops faster after losses
Raise the Barracks (stores more troops) and Quick Recruitment (reforms them faster).
WhereStronghold › Infrastructure
Keywords
Other needs · Grow my armies