Dialogue is a wonderful tool: it can be used for characterization, worldbuilding, advancing the plot, and so much more.
Here are some common pitfalls to avoid when writing dialogue:
VOICE
Maintaining a consistent voice for characters ensures a realistic conversation. Think about where your characters grew up and who they interacted with. There will be syntax differences between native speakers and second or third language speakers. Upper class characters may speak more formally than those from lower classes, and children will speak differently from adults. Cultural roots and dialects may impact the way a character talks. Characters will make different connections and use different metaphors when talking. See here for more ways to develop characters.
Think about words like “maybe” and “perhaps,” two synonyms that two different characters may use at different frequencies. Other words like this include “likely” and “probably,” “yes” and “yeah,” and “I suppose” and “I guess.”
Another thing to remember is just because one character needs cheering up, doesn’t mean a boring character will begin spouting jokes. A character won’t suddenly become inspirational when another character is on the verge of giving up. Make sure your character speaks the way you expect them to, not necessarily the way the other characters in the book need them to.
INFODUMPING
This is when you want to get information to your reader, so you have your characters talk about things they already know. Think about how you speak with your friends and family. Would you tell your sister about her sweet sixteen if she remembers it just as well as you? Probably not! You might vaguely reference a funny incident from that day. Now, if you want your reader to know everything about that event, you might have the narrator think about it or share the story with a friend who doesn’t know what happened.
TAGS
Dialogue is most effective when the reader knows who is speaking (go figure). Dialogue tags can slow down reading and writing. To prevent the latter, I tend to write my scenes almost like a play at first, just noting down who says what. Afterward, I go through and add tags as needed.
It is important to note not all lines of dialogue need a tag. If two people are arguing, once you establish what side each person is on, you can lose the tags for the majority of the scene, because your reader can figure out who is talking based on what they are saying. Another way to show the reader who is speaking is having characters address each other. Obviously, John is not going to say “John, what are you doing?” (unless that’s your story) Therefore, the other person must be talking. Remember, however, people don’t usually use names when speaking, so use this sparingly.
It is also important to use different kinds of tags to avoid being repetitive. For instance, you can use speech tags (e.g. he said, they yelled, Lea whispered), action tags (e.g. John sat down, her cheeks burned up), or both (e.g. Tina asked as they entered the room). You can also change the position of the tag; it can be before, after, or in the middle of a line. Overall, variety rules.
PUNCTUATION
Change paragraphs every time you change speakers. Use quotation marks around words said by a character. When punctuating a sentence of dialogue, periods are used if dialogue is at the end of a sentence (or is the only part of a sentence) and commas are used if dialogue is in the beginning of a sentence. Question marks, exclamation points, dashes, or ellipses can be used in either case. These punctuation marks are placed inside the quotation marks.
Using dialogue well can greatly improve your overall novel, giving your reader a better reading experience.