Here’s another simple issue that I see all the time – dialogue that sounds stilted and unrealistic. The most common way that this problem presents itself is with a lack of contractions. People use contractions constantly in their daily lives, so it sounds much more natural to say, “I’ll send you those documents when we’re done with our meeting,” instead of, “I will send you those documents when we are done with our meeting.” You should only write out the separate words instead of their contractions perhaps for emphasis or if you're trying to create a specific effect. But when in doubt, use contractions.
The other way that I see stilted dialogue is when people try to write highly stylized, painstakingly witty conversations instead of more natural-sounding ones. As screenwriters, we have the envious opportunity to write the things that we wish we could say in real life. We can be as witty, clever and even confrontational as we want without having to come up with all those mots justes in real time. (BTW, I wrote "mots justes" to show just how pretentious it sounds to write words like that in dialogue without a specific reason. Yep, that's totally what I was going for. Honest.) However, we have to be careful not to take this cleverness too far because it’s exhausting for a reader to slog through page after page of over-written dialogue. It comes across as fake and unrealistic and makes it seem like the screenwriter is trying way too hard to demonstrate how smart he is. If you want to write clever dialogue, then stick with conversations that are intelligently realistic.