Aim for the Boss during battles. Rush your entire force to the top of the stage to encounter the Boss. You will complete the stage after it has been defeated. This is not applicable in stages with time limits.
Food
After a battle, the health of all your fighters will need to be restored over time. To improve their recovery rate, either upgrade your houses or feed them food. To get more food, go to your base at the oak tree and tap the mushrooms at its roots and birds' nests in the branches to get consumables that will respawn. Animals such as deer and rabbits will appear on the battlefield. If you are safe, shoot them to collect meat to eat later.
Leveling
Watch your villagers' experience and level them up when possible. This will allow them to equip new weapon and make them more powerful and useful in battle. Also make sure to upgrade your workshop when possible.
Silver
Raiders' huts accumulate of silver over time, which is used to train and arm them. Collect from the huts often, as they can only hold a limited amount of silver.
Trader
After rescuing the Trader, visit him often. You can purchase powerful weapons from him without having to upgrade your workshops. The Traders' stock change every so often.
Villagers and heroes
As you finish additional stages, you will be rewarded with new villagers as well as be able to unlock more heroes and jobs. Keep an even number of villagers for every job. Send your slowest walkers or your short-ranged offensive units such as swordsman to be in the front line by controlling them manually. Other units will follow you automatically to the enemy which you are attacking.
Weapon specialties
Raiders can change their weapon specialty at the Academy. You can increase the number of archers or swordsman as needed by changing their specialties.
Battles...