One of those interesting linguistic terms that I don't see talked about much is register. What is register, you ask? It refers to the different ways we talk to people in different situations. For example, when you're with your friends, how do you usually speak? Loose, informal, more contractions (can't, won't, wouldn't've)? Do you shorten and conjugate words irregularly, like "gotta" and "wanna"? Do you ramble in long, run-on sentences about that hilarious story you heard that you've been dying to tell everyone? We tend to be more relaxed in our speech patterns are well as our body language when we are in situations that make us comfortable, such as when hanging out with close, trusted friends.
Now, compare that to how you speak in a business setting. Maybe you're at a job interview, and you're on your best behavior. You might enunciate more clearly, stressing syllables you usually slur. "Gotta" becomes "got to", "wouldn't've" becomes "would not have." Or remember when you were a teenager (perhaps you still are) and your parents would introduce you to their friends. Were you nervous? Did you speak in short sentences, maybe act more polite or surly depending on how much you cared to impress them? Quite a difference from those long conversations with people you know well, right?
This is register, and it is an invaluable tool in your writing. Your characters are ultimately pictures of people, and so they should talk and act like normal people would if you want your readers to believe in them. Is your character more comfortable in a quiet, private setting with friends, or does their personality really shine in the middle of a hectic party? Or do they put their strongest foot forward in the boardroom, dictating commands to a team of scurrying office workers? Maybe they act with utter confidence while sending a battle cruiser fleet against an alien incursion, but become reserved and uncomfortable at awards ceremonies. How your character acts and how their dialogue flows can get this message across to your reader without you having to spell out where their social strengths are. That, in the end, will help to make your character into a lifelike, relatable figure who your readers can invest in.
