Here's my current thoughts on a turn sequence for fast-paced activities, such as combat. By fast paced, I mean those times where the rate of irrevocable, bad things happening outstrips the party's ability to integrate what's going on, talk it over, and come up with a plan that takes into account everything they've perceived.
Those times when, suddenly, arrows are skewering the hirelings, one of the ponies bolts and—for some reason—Cyril's on fire. Bad things are happening, quickly.
The adventurers have to act now, on partial information, or risk being cut down while they're taking it all in.
So, some design assumptions.
First of all, turn length is somewhat plastic. A player's turn might represent a few seconds in melee, longer in plains chariot warfare, or half a minute in an archery duel at range.
Secondly, this is theater of the mind combat. There are no miniatures to tell you how many enemies and where they're standing, or even where all your companions are standing; to get that information you have to look. If your turn consists of dragging Cyril to the side of the bridge (which is hopefully sheltered from whatever the hell is happening), all you get description about is Cyril. Obtaining information about the battlefield costs time, and maybe lives.
Thirdly, turns aren't simultaneous, they're sequential. Shocking things are happening quickly enough that most of the party is simply hesitating: summoning up the gumption to run through the hail of arrows, mind overwhelmed with which direction is safest, looking from Petryn to Garom, seeing what the party's most experienced warriors are starting to do, wrestling with the instinct to chase after the pony, or just standing in shock, listening to that god awful noise Cyril is making.
When Petryn charges forward to engage that shadow behind Cyril, the green and awed recruits just watch him go, at least for now.
Fourth, while the players have to take turns, every time they do, all the baddies go at once. When Petryn charges to cut down that shadow, the shadow gets an action, as do the unseen archers, as does the troll climbing up over the side of the bridge. It's not looking good for Petryn.
At least, that's true in an ambush. Several things modify this default, horrible situation: initiative, cohesion, exertion, leadership, and preparations.
Initiative is the readiness and wherewithal to start decisive action. It's held by one side or another - the side with the initiative is choosing the bad things that happen, and forcing the other side to react. The side without can't form plans of their own, at least not without suffering terribly as they ignore the enemy side's moves.
If the adventurers have the initiative, they'll have a moment to decide whether and where to strike, rather than simply screaming and trying to hold the line as the shock troops come crashing down on them. When the enemies act, there's a beat where they telegraph their moves, drawing swords before they charge, aiming before they fire, letting an organized party adapt and pre-empt them.
Cohesion is the somewhat abstracted, physical arrangement of the party. They may be ready to act, but are they placed to act together? Did they get spread out while crossing the bridge, as the foragers took a moment to look down into the valley. Did Garom stop to make water by that tree stump while the rest moved on ahead?
When a cohesive enemy has the initiative, they act decisively and in unison, and they'll do something bad. Maybe they unleash a volley of arrows at every single party member; maybe ten of them all charge Garom, who is forced to meet them alone. When the enemy lacks cohesion, they act piecemeal; a few charge, a few retreat; some bellow orders while others shout competing ideas.
Exertion is a per-adventurer resource that lets them interrupt the turn sequence. A point of it lets you join someone else's action (say, charging in with Petryn, or helping to drag Cyril), and two points of it lets you interrupt completely (e.g. going before Petry or anyone else to plant an arrow in the troll's face as it crests the railing).
I'll get into the details of exertion another time, but suffice to say it's a precious resource that adventures have in very small quantities, more if they're rested, and much less if they're burdened with armor, gear, or the duties of travel. Exertion can represent a heroic burst of adrenaline-soaked speed, or it might represent sustained vigilance - say, that you had your bow out all along, because you've had a bad feeling ever since leaving Grunford.
It's a little bit reconny in the sense that it can establish details in the recent past, but just a little - not so far back that it would seem out of order if it was a two-second shot in a movie's action sequence.
Lastly, leadership and preparations. If it's been established that the party is only waiting for Petryn's signal to break for the south end of the bridge, then if Petryn does that, the cohesive parts of the party can all act in unison. The plan might be to run for cover, to fire a volley of arrows, or to do several things at once.
Leadership is the second best thing - an impromptu order from someone with the party's trust can galvanize some of them into action, at least as long as the trust and confidence are equal to the chaos at hand.
The point of all this is to really double down on perceptual play, emphasizing the difficulty of integrating a complex situation. A party with a plan, the initiative, proper placement, and with a strong leader to issue orders when things go off the rails can be devastating. They act together, steamrolling the enemy piecemeal, while the opposing side struggles to make sense of what's happening and acts as a fragmented mess.
A party that kicks in the door is just going to get chewed up immediately, taken out by enemy actions they only recognize after it's too late, if at all!