Read your work out loud!
I have read this advice somewhere, heard it from someone, and disregarded it, until one day I went to see Chuck Palahniuk and listened to him read his short stories and talk about the importance of reading your own work. Out loud. I came home and tried reading what I wrote. I was horrified at how bad it sounded. Every time I'd stumble, I wanted to change it, to clean it up, to make it better. And, on top of that, I relized I saw flaws that weren't visible before.
Above is my 1st video of me reading from current work in progress, a YA novel SIREN SUICIDES.
I need to do a lot more of it, AND you do too, AND here is why:
Practice to wow your readers. That day will come, when all your dreams come true - in the shape of a published book that you can hold in your hands. Guess what, now comes the publicity. You will be asked to travel to literary houses, libraries, conventions, conferences, you name it. And, *DRUMROLL*, there you will HAVE to read your work out loud, to an audience. Scary, isn't it? I know, I'm scared too. Doing my first public reading tomorrow at Hugo House and scared out of my wits. But I will have to get used to it!
Hear what you couldn't see. You will come across places that sound wrong. Just plain wrong. Either the sentence is awkwardly constructed, or the word sounds weird, or there is a sudden repetition. Whatever it is, if you stumble on it, you've got to fix it. You will hear what I mean when you read it. If you want to go one step further, have someone else read it to you. The effect will floor you (the other person will stumble on places YOU didn't).
Write better dialogue. Because dialogue is really our feeble attempt at capturing the essence of the spoken language, it's a MUST to read it, to hear how it flows, to make sure it sounds the way you'd tell your friends about something. If it feels wrong, rewrite it. Take the idea your character is trying to get across and say it in other words, simpler, see if it sounds better. If it does, presto! You just made your book THAT much better.
Refine characters by acting. This is an interesting side-effect and perhaps it's only something that happens to me, but I've noticed that reading while writing helps me refine my characters. I would get into a particular tone of voice when reading for one character, then switch to another tone when reading for the other. It even works for setting descriptions - I would pretend to be the town or the rain or whatever else it is I'm describing. If it sounds out of character, I know I need to fix it.
Have fun! Yes, this benefit might be overlooked, but we all get to that dreadful place called 'writers block' or 'bad mood' or simply 'I'm so burned out or lost or whatever, I can't do this whole writing thing anymore.' Been there, done that. Guess what, when you read your own work out loud, it starts sounding like a story separate from your anxiety, it takes on a life of its own, and it gets you excited again. It gets your juices flowing, you want to know what happens next, and within minutes you somehow, miraculously, are back to writing. Try it, works like a charm!
There are probably many more benefits I haven't touched upon. Feel free to add more in the comments!