Kirroki
I don't know how to write battle scenes. Most of my stories involve them. I've read many stories and watched lots of movies and shows with battle scenes but to no avail.
One story in particular has been the most difficult. It is a space venture with a kind of Star Wars feel. I have no idea how to go about writing a major battle scene. I'm not talking about one-on-one battles but army against army.
The Basil Broketail series has some good battle scenes. In them the basic movement of regiments are noted, and then the particular valors of specific people are presented in detail.
If you are really talking about army against army, study major historical battles. Waterloo, WWII, The Revolutionary War, the Campaign of Alexander the Great, etc... Then you'll get a basic idea of how regiments move (which I think is of major importance). The Illiad is another good source.
Also, concentrate on your point of view. Will you be writing the story with a focus on individual fighters, or will you be recording a major battle without any particular details to them? I hope I've given you some ideas.