Why shouldn't you use the word "very" in your writing?
Avoid using very in a sentence because it's a weak word that diminishes your meaning. It's commonly used to intensify a weak adjective or adverb, but there's not enough information in the word. You're better off finding a stronger alternative.
Consider these sentences:
The very large dog's hackles rose.
The monstrous dog's hackles rose.
The second sentence uses a stronger adjective that relays more information to the reader.
Here's a great list to replace very + weak adjectives with strong adjectives that will pack a punch in your writing.