The aim here is simple, allow patterns of combat behavior to be expressed as an extension of organized groups and their leader's tactics skill, or the militia commander's (player's) orders. This specifically concerns specific squads, or nearby groups of allies who happen to be rallying together. Many of these should have elements in the military menu.
Combat-arts would be actions on an individual basis. For instance, wrestling and charging both count as combat arts by this metric.
Situation Tactics
Assess enemy: an action that can be taken by those with high military-tactics skills, this allows the respective squad (or fortress) they're in assess the skill level of hostile and neutral units. Those with very high skill can determine with more specificity, and sometimes before the target even attacks.
Scouting: This tactic can be assigned to small squads, particularly for the purpose of the "assess enemy" action. They will try to use their ambush skill, attempt to avoid the enemy's bearing as opposed to simply remaining a distance from them (project where the enemy is going, and avoid that path), and potentially take pot shots at them with ranged weapons. If spotted, they will sprint away, usually to a "place of retreat". Scouting dwarves will use their observer skill to look for hostiles who are likewise sneaking.
Place of retreat: defined areas in which squads will attempt to retreat to when called for. These can have different levels of defined "security", and squads will tend to prioritize higher security retreat locations if they have several to chose from within similar distance. Security levels and locations are defined in Fortress Mode like burrows, and in worldgen towns exist as their associated regions in towns (pubs, barracks, inside buildings, quarters, castle, etc) Security ratings are arbitrary, and set by the player in fortress mode.
Staggered retreat: dwarves will seek the closest shelter available and defend it. If their current shelter is being overrun, or after a quick look around a corner they determined they can retreat to the nearest shelter with higher security rating, they will retreat further to that location.
Withdraw: The squad will hold a tight formation, (careful not to push their allies prone with pathing unless it's down a 1 tile hallway), relatively slowly retreating to designated place of retreat. When engaged, the squad will prioritize defensive maneuvers and continuing to move further back, unless they are confident they can make quick work of the unit they're being engaged by, or have a confident crippling shot against that unit available.
Combat-art: Dwarves with high shield skill can attempt to block hostile projectiles that are passing through squares adjacent to them. Dwarves who are adjacent to hostile archers can directly "parry" their shots, that is to say, strike their weapons so that any hope of a good aim is lost. Archery weapons ought to be relatively fragile if struck when strung, possibly disabling it for archery purposes outright.
Rout: A squad has completely lost morale and stopped listening to their leader. Members will individually continue fighting as if in swarm, or run away in attempt to break line of sight with hostiles as soon as possible. Once line of sight is broken, units will move towards the nearest place of retreat until their morale restores. Leaders use the related social and leadership skills to restore this morale and can be ordered to seek and rally disorganized troops.
Engagement Tactics
Low-risk tough target: This tactic can be called for when there is a particularly durable, dangerous, but unskilled target. Dwarves (or whoever is using this tactic) will attempt to approximately surround the unit to prevent easy escape. There, they will attempt to attack the unit as normal. Dwarves suffering from very low stamina, nausea, or other debilitation will withdraw temporarily, or retreat outright for significant injuries (pulping, bone break).
The intent of this militia art is to help dwarves who are poorly equipped take on large animals with little risk, assuming the animal is basically crippled by it's low stamina. Specifically, it's to prevent dwarves from attacking a unit that isn't a major threat until they themselves fall unconscious, where they are vulnerable to killing-blows in the brief moments the hostile wakes up. This also applies to the likes of highly skilled squads trying to face off with megabeasts.
Intervention Arts: When a dwarf isn't being directly targeted and grappled, their highest priority is to attack the limbs of nearby targets being used to injure their allies, assuming there are somewhat confident hits to be made. This tactic is a call against wrestlers and large creatures with bites alike. If an enemy is standing over a prone ally, a dwarf can either try forcing the hostile off of them, damaging the hostile's legs, or "dragging" their ally out from under the hostile as a combat-art.
Swarm: Current normal combat behavior, requires little training or morale to maintain.
Subdue: Dwarves will attempt to subdue the target while keeping them alive. Edged attacks are avoided, and dwarves will attempt to wrestle and pummel the target into submission. As a combat-art, a dwarf can be equipped with ropes, chains, or a cage in which to trap the target when they are unconscious or over-exerted, but will be instantly interrupted by incoming attacks when attempting to do so. Hostiles can request quarter which will allow them to be captured earlier. Dwarves against dramatically powerful units will be too intimidated to subdue and capture them in this manner, unless they request quarter or are already unconscious. Will basically not be used against groups of enemies.
Hold Ground: Dwarves will attempt to defend a tight location, refusing to advance beyond where they are assigned to to engage enemies. No acrobatics through fortifications allowed either, though dwarves may attempt to seek cover in obstacles in their defensive area to help against ranged attackers if they can't shoot back.
Cover: Like Hold Ground, but dwarves will go prone until there is an enemy unit within a few tiles range. If they have not been engaged yet, they will be in ambush mode. This is specifically to reduce the chances of being hit by oncoming archery fire before engagement, but can be used by archers and soldiers alike to ambush enemy squads in the forest.
Those are my ideas so far. What do you think? Do you have any ideas yourself? Make sure to take into account how Dwarf Fortress works so far when you ponder your idea.