Phases Of Battle Edit
This is a generalized strategy that I developed during my first playthrough of the game. I think it will be helpful for folks new to the game or who are simply struggling to get past a difficult wave.
Phase I - Staging Your Bannermen & Conducting Research Edit
I think it's safe to say that you should start every battle with at least two Bannermen on the field. You are seriously handicapping yourself by having slow Command Point growth if you don't do this. If you are fighting a very slow enemy or an enemy you can fend off alone you might want to hold out and get your third Bannerman. Once you have at least two Bannermen on the field, you move onto phase 2.
It goes without saying but once you have Research unlocked, immediately choose your research items at the start of battle.
Phase II - Autosummon & Building Ground Units Edit
Choose one or two ground units you want for ground support and set them to autosummon. Autosummon allows you to automatically summon units once you have enough Command Points to cover the cost of the unit. To autosummon, just press the icon of the unit until the icon's border changes to green. To remove autosummon, press the icon until it's border changes to tan. The order autosummoned units spawn on the battlefield is determined by the order you selected units to become autosummoned.
The primary advantage of autosummon is that it frees you from focusing on Command Points and deploying of new units. This is very helpful if your hero is fighting enemy units. The disadvantage of autosummon is that it's removes some control in the manner you deploy units.
Balance the time you spend protecting your walls and Bannermen and the time you spend deep in the battlefield eliminating enemies. You need to eliminate enemies to earn experience but you also need to be mindful of enemies spawning close to your walls and Bannermen. Unprotected Bannermen can be eliminated and will set you back in your Command Point production.
Once you have a population of 8-12 of ground units and/or have sufficient control of the battlefield, move onto the next phase.
Phase III - Midpoint of a Long Battle Edit
For long battles you will need strength in numbers and fast Command Point growth. If you are managing enemy mobs with your hero and your ground units I suggest the next units you autosummon are Bannerman and a wall unit (in that order). Keep autosummon activated on your ground units.
If there is a fear of getting overwhelmed by enemy mobs autosummon a low cost ground unit to occupy the them; Blunderbuss, Iron Helm and Footman are good choices.
If you have not set autosummon on the Bannerman, at a certain point you should do so. Over the course of the battle you'll get more enemies and more powerful enemies. It is important to maximize your Command Point production before the enemy starts to ramp up their assault. Faster CP production means faster unit production.
If you notice your Bannermen are getting killed in battle then it is very important to level them up. I consider the Bannerman the most important unit to level up early in your first playthrough.
Phase IV - Clean Up Edit
You have almost maxed out your ground and wall unit populations, now might be a good time to invest in Support Units. A priest or Elven Healer can heal your units and a repairman can repair your walls. Obviously choose the option that helps you the most.
Phase V - Lay Siege to the Enemy Fortress Edit
During battles that involve destroying an enemy fortress you might want to invest in "siege" units. Siege units will assist your assault on the enemy fortress. Early in the game you'll get access to the Plainsman. Use the Plainsman until better units become available.
During battles that involve conquering new territory from the enemy I will deploy a healthy mix of ground, ranged and support units to fight the enemy mobs while I use my hero character to rush the enemy fortress. A hero with the Knight Sword Strike skill can destroy wooden enemy walls with just 3-4 attacks. Rushing an enemy wall without friendly units nearby will make you an easy target for enemy wall units. If you are running low on healthy while rushing the wall, run to side of the enemy fortress. Enemies may follow you there but you'll have breathing room to deal with them and you won't be attacked by wall units.