One of my friends on Facebook recently asked: How do you get the mechanics of fight scenes into stories, and construct them well enough to keep people interested, and the scene exciting?
First you have to build conflict. And conflict always starts light and builds over multiple scenes. For instance, in SHADOWS IN THE MIST, my main character Lt. Jack Chambers has an antagonist named Lt. Fallon. They have a bad history, so I use their past falling out to create some immediate tension. From the moment they get assigned to work on the same mission, they don't like each other. I create tension in their dialogue as they take a few verbal jabs at one another. Every scene that follows, Chambers and Fallon argue more and more. Later their hatred builds to the point that they're slugging each other. All this builds up to them battling in a climatic scene with weapons. So, the key is your protagonist (hero) must always have an antagonist (villain) who oppose one another. No matter how much they dislike each other from the beginning, start building conflict slowly, light to heavy.
Another thing is your protagonist and antagonist have to have a reason they hate each other that's believable. A common reason is two men are in love with the same woman or are competing for the same job or are on opposite sides of a war. They are enemies competing for the same prize. The opposing characters can be between two women (as in the movie BRIDE WARS) and also between a man and a woman (ROMANCING THE STONE or FOOL'S GOLD). The tension builds as they go from bickering at one another scene after scene until it builds into a heated screaming match. This also builds sexual tension, which is why the man and woman end up tearing each other's clothes off. That's the formula for a great romance novel. They dislike each other from the start, have opposite viewpoints, bicker, argue, fight, have passionate sex, and then fall in love.
The next time you read a book or watch a movie, notice how the conflict builds over time. Notice by the time two people are screaming at each other or fighting with fists or weapons, you the viewer are ready for that action, because it's been building in every scene prior. When you build conflict scene by scene in your novel, then the actual fight scene happens naturally. Your characters will take over the story and let you know when they're ready to duke it out.
In answer to your second question, the way to keep your reader interested is you create believable characters that are human and passionate about opposite ideals. The protagonist and antagonist are so headstrong that they'll do whatever it takes to get their way, and they are righteous about their viewpoint. Watch the movie DOUBT. It's classic conflict that builds into a brilliant verbal match between Meryl Streep and Philip Seymour Hoffman. When two of my characters get into a fight, I always ask myself, what's the worst thing that could happen that could come out of this? What would be the worst outcome for each character in the fight? And that's usually the way I write it.