When I was fifteen, I had a teacher whose name was Mr. Campanale, and he changed my writing forever. This is how he did it:
1. We would sit and look at my sentences.
2. He would point to a word and say "Do you need this?"
3. The answer was always no.
There are many talented writers who use lots and lots of words, and there are also times where lots of words are necessary. But I think most people use too many fucking words, and that lots of them mistakenly believe that that is what makes good writing. If you ask me, you should not only use fewer words, you should use as few as possible. Here are some reasons why:
Just as it's good for an actor to have a secret -- something that makes them a little inscrutable and excites the audience -- it's good for a writer to have at least one. If you've got too many words on the page, you're probably giving things away when you don't need to be. Let the secrets inform your choices, and don't feel like you need to always tip your hand.
If you've got too many words and you're not explaining too much, you're over-embellishing. That quote attributed to Coco Chanel -- "take one thing off before you leave the house" -- applies in every artistic discipline. Because too much stuff creates clutter and noise, and the good parts lose their impact.
Supposedly, Dorothy Parker sat next to Calvin Coolidge at a dinner and said, "Mr. Coolidge, I've made a bet against a friend who said it was impossible to get more than two words out of you."
He said, "You lose."
I had to look up Dorothy Parker's half of the conversation; I've always remembered Coolidge's.
All theatre is teamwork, including playwriting. Even when writing alone, you are collaborating with your actors and director. (Through time and space! You are magic.) Leave everyone room to do their job. I talked about that here, with respect to stage direction and design, but it's true in dialogue, too. By explaining less, you leave your actors more room for secrets and your director with more questions to ask them.
Okay then, asshole, what's your point?
When you write your shit, look at it and say to yourself, If I take out this word, does the meaning change? If the answer's no, take it out.
And by "meaning" I don't necessarily mean intelligibility. Maybe what you want to get across is "this guy's nervous and he's blabbing about nonsense," and that's a legitimate thing to communicate. So I'm not saying you need to get rid of the blabbery; just make sure you're using the best parts of it.
This is something I still work at, and I think a good example is my 2008 play We Three. There's a long monologue at the end of the first act, and I know, looking back, that it's too long. I got too excited about what I could do with that monologue, and I overwrote. Maybe this week I'll see how much I can cut, and give you a before-and-after.