Larger scale battles have to be written a bit differently than normal battles. One difference I notice in the better ones is that the description of what is happening, tends to be what is happening around the protagonists, as well as what is happening to the protagonists. Focus seems to be more on the overall feel of what the characters see, as opposed to what they are doing. The exception of course, is when the character is directly involved in combat against another enemy. In cases like that, care needs to be taken to properly describe the individual fight, while still showcasing how the battle is progressing (though in this case, more focus will be on the immediate fight).
I won't lie. This isn't an easy thing to master, and is indeed among some of the harder aspects of writing that there are. At least, that's how I see it.
A Winner Is You!!!
If you spend too much time thinking about a thing, you'll never get it done.
- Bruce Lee
It is amazing that people who think we cannot afford to pay for doctors, hospitals, and medication somehow think that we can afford to pay for doctors, hospitals, medication and a government bureaucracy to administer it.
- Dr. Thomas Sowell