I am not good at writing dialogues, so I want to write as little as possible while making the story engaging and having good story beats. I would like to know if there are good ways to know whether a dialogue can be cut or not, and how do you determine if there's not enough dialogue in a story. Is there some golden rules or rules of thumb that can be used to determine this? What are some ways to cut dialogues and some examples that show this can be done without hurting or perhaps even improving your story?
One rule of thumb is to delete pairs of short snatches, between pairs of characters. Look through the dialog, scan pairs, and see if those can go wholesale and still make sense.
A second rule of thumb is to avoid info-dump through dialog, and avoid 'as you know, Bob' dialog. Dialog is a great way to bring in unexpected information, naturally. But this is not an excuse to dump information. It's more the case that because every speaker has a unique personality, and a past with the other characters, and so, surprising snatches can move things quickly... unlike the narrator who has only a single personality and is basically there in conversation with the reader.
The group entered the tavern. It was much like all the others, with a fire, the punch of wood smoke, and fair wenches strolling hither and yon.
"By all that's holy," Bri said. "Is there not a single tavern in all of Havensbrook where the men serve ale?"
"Quit your griping."
She looked around the tavern once more. "We'll need a bigger boat."
... what? But dialog can do that. So that's something to keep in mind, that these characters have an ongoing relationship and understanding with one another. Play with jumping.
As far as metrics, look at https://creativityhacker.ca/2013/07/05/analyzing-dialogue-lengths-in-fantasy-fiction/#:~:text=The%20texts%20of%20the%20majority,Empire%20(Mistborn%20%231). Aim for 13%-37% dialog.
I would check out Margie Lawsons EDITS method described in her Empowering Characters' Emotions. This package is not free but in my opinion, it's well worth the money.
Lawson has divided the literary text into several different components, dialog, description, etc and she discusses rules for distributing them in the text. For instance that a scene should start with some description.
However, the overall rule is to mix different types of components. The EDITS method is about color-coding the manuscript with highlighting pens. Then you place it in front of you and if you have page after page of the same color, you can tell you need variation.
A part from that, I know of no rules per se, it's more about feeling. Or, for that matter, listening.
Read your text, or have your computer read it (if you're not quick to cringe...) and you should be hearing if something drones on and needs to be cut out.
However, dialog is one of the greatest tools not only for showing character but also to up the tempo of the text, so if you don't feel the text is babbling on or getting stuck, I suggest aiming for more dialog rather than less.