Fight scenes can be daunting to write. In simple terms, the conflict in your story manifests as physical violence in an all-out fight. Here are some essential tips for writing good fight scenes that hold your reader's attention: 

Plan your fight scenes in advance: 

Fights don't happen randomly. Your character fighting another character could leave your reader confused and lost. There needs to be a specific progression of the plot in the direction of a fight. Hence it is always a good idea to plan your fight scenes to fit the motivation of your story and help it progress. 

Short sentences and scenes: 

Your sentences create rhythm in your story. Long descriptive paragraphs slow down your fight scenes and force your reader to stop and visualize the details. Using shorter sentences gives them a sense of things moving quickly. Action should be followed by another action before they have time to process the previous one. A brief fight scene with short sentences hooks your reader and gives them just enough thrill to make an enjoyable experience. A fight scene that drags for too long gets boring eventually. It is a good idea to keep your action short and crisp.

Mix dialogue and action sentences: 

Action can be followed by dialogues and conversations between the fighters, as continuous action is prone to redundancy. Adding dialogue contributes to the characterization of your characters and hooks your reader's attention. However, monologues and introspections don't work as the character barely has time to react in a high-paced situation, making self-reflections highly unrealistic.

Use a first-person narrative: 

Third-person narratives give a logical, disinterested view of scenes which can quickly make your fight scene boring. Utilizing first-person narratives offers insights into the character's immediate thoughts and reactions. Their convictions could be revealed through a fight scene as they don't give the character much time to react or consider their actions. 

Play with all the senses:

Passively reading about characters punching each other or hitting each other with lasers gets old in no time. The repetition can make your scene flat and exhaust your reader. So, instead of telling readers about the river beside which characters are fighting, describe the scene with 'the sound of the river punctuated their heavy breaths,' or 'there was a faint metallic taste in my mouth.' These images trigger the hearing and taste senses and make the scene more believable. Touch can be employed by describing the feel of the ground, sand, or any other surface that the character falls on after receiving a hit. Your action doesn't have to stay confined to kicks and stabs.

Resolution: 

Your resolution should have meaning to it. By meaning, I don't mean that a significant physical change has to occur in the world or any of the characters involved in the fight. I mean that after a fight, there should be a change. The change could occur in a character's mind, give them peace, or continue to trouble them. In the end, the fight must have an impact, for, without it, the fight scene is essentially meaningless. 

It is always good to get opinions from your friends or other people you know to understand any shortcomings in your setting and their effect on the reader. At the end of the day, a fight scene is like any other important scene in the book. When well-written, it will be fascinating to read it. It must always arise out of the plot's need and work toward fulfilling the story.