Some people go overboard with dialogue. Kate from Author2Author lists a few things to be aware of when writing dialogue including the big one: Dialogue slows pacing!
I recently posted on the Functions of Dialogue. While this post from The Blood-Red Pencil is similar, I love the delivery of this information and the fresh perspective. I think it's worth a read, even if you know the functions of dialogue.
And a few last minute tips:
To use dialogue to create conflict, you can list what each character in the scene wants and try to find two things that don't match up. For example, Penny wants to wear red, but her husband wants her to wear black. This can also help you throw in some interesting situational conflict. For example, maybe Penny's red and black dresses are dirty or stolen or not warm enough for the weather. Suddenly, the two of them are scrambling to make their preferred color dress wearable. (Penny throws her red dress in the wash, while her husband looks for a black shawl to put over the sleeveless dress.)
...Or something. This is just an example off the top of my head. :)
If you find your dialogue is stiff or unnatural sounding, put yourself or your best friend in the character's shoes. What would you say if someone told you XYZ?
If that doesn't work, try listening in on other people's conversation. As politely and discretely as possible. (Note: ONLY do this if your dialogue is too formal. It's not ideal if your dialogue lacks conflict.)
Any other tips? What do you do when your dialogue is stuck?
More on Dialogue