One problem a lot of novice writers make with their dialogue is they put in too much extraneous conversation. It’s important to understand what to leave out. An easy way to do this is to ask yourself, why is this conversation important? If your characters are meeting over lunch, skip over all the discussion about the menu, what to order, hold the mayo, pickle on the side, blah, blah, blah. Get to the point. Unless it’s important to the plot or helps with character development, who cares if your character tells the waiter to put the salad dressing on the side? Most of the time it’s not important at all. So begin the scene where the important discussion begins.
Another thing to watch for is anything that breaks up the flow of the conversation. Anything that makes the reader stop and say “Huh?” needs to be fixed. This generally happens when someone says something they wouldn’t say or does something that doesn’t make sense. Dialogue should flow and not be interrupted by a lot of stops and starts. I’m not talking about pauses while the characters react to something or do something that is important to the story. I’m talking about breaking up the dialogue with unnecessary descriptions. If the dialogue is too fragmented, then you may be putting in a lot of extra words that aren’t needed. Go back and read for content. Does it advance the plot or provide insight into the characters? If not then you should cut it.
Pacing is also important. If your characters are talking over lunch, don’t have the food arrive then be gone after only a few comments. Think about how it would happen in real time and write it that way. If it only takes a few minutes for the conversation to take place, then don’t have the waiter take away their empty plates when they finish talking. Let them talk, then take a bite of their “untouched” sandwiches. Dialogue over food can be a real gotcha if you’re not careful. If the reader stops and says, “Wait a minute, when did they eat all that food?” then you have a problem.
One last point – avoid the soapbox. Rambling discourses become boring very quickly. Get the point across and move on. If you’re at a party and some blowhard is going on and on about something, you generally tune him out or move on to a more stimulating conversation. Your readers will do the same thing. Don’t bore them with speeches. Remember, you’re writing scenes in a novel, not producing a transcript.
There are only two things you want to accomplish with dialogue – advance the plot and develop your characters. Anything else is fluff. Unless you’re getting paid by the word, get to the point.