How do you improve your combat sequences?
If the fight is quick and one side is clearly overpowered and broken, then a few sentences followed by the character's or the narrator's reactions would be great. Include sound effects.
The Protagonist launched forward. Bang! With a single blow, a swift left to the skull, the villain's head imploded. A mass of blood rained down upon the crowd! First a girl screamed; then the entire crowd fled. He, he was a demon. A madman. And he was their God.
Like describing the emotions and reactions would usually place the reader in the same position. And most of the time, fight scenes are more about set ups more than the actual fight. There's a difference between a random thug getting knocked out in a single punch then Saitama just jumping into an ocean of monsters and mowing all of them down.
I noticed you mentioned elaborate though. In that case, you would really have to manage your descriptions and pacing. Like imagine if the scene played out on screen; what would you immediately notice.
Is it how big the other guy is? Or would it be the sheer overwhelming anxiety apparent on the main hero's face; or his arrogance. I think Shen Yin Wang Zuo have some very elaborate fight scenes, but the sentences themselves are usually short and simple.
You can honestly go two way with elaborate fight scenes. Simple short sentences to imitate the intensity of fighting. Describe the skills, the expressions and reactions, and thoughts of everyone in a way that you can see it if it was like an anime.
I would usually study fight scenes from other stories and see why they work. Maybe make a folder of saved chapters where there are good fight scenes.
In short, for all the questions you have asked the best answer is: Research (books/google are best friends.)
I think it's mixing up the length of your sentences, with relevant and relatable options. no need to explain every exchange in details, leave some information open so the reader can fill some minor details themselves. Short and less detailed descriptions are easier processed and imagined than a detailed description of every hack, slash and swipe.
Also, it helps if you write a fight scene with purpose to it. Simply he hits here and the other guy hits back feels robotic and bland. The fight has a narrative too. Maybe our hero is aiming for a particular pressure point. Maybe he's trying to push his opponent towards an injured buddy who can't move but has a knife. Maybe he's trying to get his opponent mad by trash talking him so he won't notice the kid hiding under the bed.
Giving the scene goals and problems within the fight helps make it feel more dynamic and more like a story.
If you're writing in first person, the action should feel harried. IE sensation; reaction; sensation; reaction; prediction; result - and so on until completion.
Fantasy novels give a bit of flex room. Characters with absurd levels of training have more time to 'absorb details of their surroundings'. However, think back to any fight you've been in ever - the results rarely match any training and often times feel more rushed or panicked.
Ready for a personal story? Too bad! We're on a drunken sharing adventure.
I took a semester of 'self defense' in college. They taught us to punch, kick, and debilitate an attacker if conflicts arose (and of course ways to back out of the combat) - during this course a police trainer showed up in fulll protective gear and said 'try to make me back off'. The actual scenario involved more words but teh gist is clear. We were put in a 'fighting' situation with this guy and basically needed to react.
I - a man who had taken years of martial arts practice - punched a lot. It was forking useless on his padded armor left, and served as an object lesson to every single confused looking college girl who followed. 'don't just blindly hit' - that being said, I as a person couldn't think of much else in the moments rush.
So, when writing - imagine QUICK combat. What do you notice? What do you have time to notice? Spell those items out FIRST - then fill in items which need to be mentioned in order to smooth the scene out. These may not directly overlap because the READER requires a few extra steps. They're likely not the hardened battled minded master that your MC is.
But if you're writing a one vs one epic fight, then switch to first person pov. In your notes of course LOL haha!! Oh well, you just write in your notes the whole fight in first person as if it's you fighting, then change it to third limited which shouldn't be too hard. Well, that's at least what I do
In a large scale battle where it's two large forces facing off against one another then I find it's easier to just focus on formations, the movement of the battlefield. Generally I find it easier to think of combat as a whole in terms of action and reaction. The MC does one thing, the enemy reacts, the mc reacts, the enemy acts, the MC reacts, the enemy reacts, and blah deh blah, blah. It goes on until everything is unconscious, dead or a side runs away.
Hope that helps :D