don't forget repetition - it can slow down the action, but it can also add a feeling of realism
or, if you don't want to be realistic, you should sounds really witty and deliberately rehearsed. im not saying shakespeare, because if you could write on the level of shakespeare for homework you shouldn't be in school, but maybe something like Gilmore Girls where the dialogue is not always well written but it's witty and - most importantly - way too quick. Actually, it's a bit like how my family talks, with all sorts of jokes said as fast as they can between real lines so as not to interrupt but still try to be funny....anyway i digress, but the main point is that whatever extreme you choose to explore, the dialogue should never be see spot run.