Fighting, is pretty basic, there's just certain mechanics you have to master to become the best fighter in Minecraft. The first thing is tracking/aim. Minecrafters will always jump and run around when PvPing so you have to be able to hit every hit to win every fight. There's a hidden tactic though, to have really good aim tracking. All it takes is one task which is, get to download an auto-clicker. If you can click on them faster than they can click on you, you can combo them to the point where they can't hit you.
Download an auto clicker Here
In minecraft, you have to be willing to take risks and not be afraid of taking fights. You should watch at least 1 horror movie before entering so you will not be afraid of fighting other players or mobs because you will be afraid of the movie.
Once you do that, you are 2/3 the way to being the #1 Fighter on Minecraft. Still, there is one more task, this task might be one of the easiest ones, you need to be able to find a good server to fight on and practice.
After all that you have done, you will become the best fighter in Minecraft. But there is one thing I forgot to tell you, there is many hackers on Minecraft so you will lose some battles if going against a hacker.