"Why do TV characters end phone calls without saying "good bye?"
My quick answer was, "it's done because of 'time aired'. It doesn't move the plot forward and is unnecessary Most viewers don't notice. It's telling the reader what is already obvious and doesn't need to be in the script". Or something like that...
So, this point about dialogue is particularly important
The idea is to cut two of every three lines of dialogue that would occur in a natural conversation in real life.
It is a bit. Not the cutting/deleting words bit (that's the easy part). The hard bit is the rewriting so that it makes sense. This is how you make your writing tight.
Take a look at this simple example:
We're going camping wanna come?
I've got a bad feeling about the weather.
You worry too much?
Okay, so writers need to keep it tight.
Another part to this is, 'avoid "yes" and "no" in your dialogue'. Imply it in the answer. It makes dialogue stronger.
A real example from Game of Thrones
A: You trust me, Jon Snow?
Jon: Does that make me a fool?
A: We're fools together now.
Of course, this doesn't always apply, sometimes a short "Yes." might be even better. But try it out on your own story and tell me what you get.
Are you still feeling a little rattled?
Here's some encouragement from Zen in the Art of Writing by Ray Bradbury. Ray says "...you can't write 52 short stories in a year (one a week) and make all of them suck. At least one of them will be good enough for you to rewrite".
To try this you need to write one story every 7 days. If you struggle to finish a story by the end of day 7 simply write a terrible ending, or spend another 7 days on the same story and adjust your goal.
NOW, go write!