Jargon peoples! Yes, the lingo, slang. Jargon. What types of special jargon or lingo do your characters use?
One of the things pounded into our heads as writers is that every character has their own unique voice. Unique voice includes the catch phrases or special words they might say. Jargon can come into play based on where your character grew up, what type of education they have, or what job they work.
The warrior elves in my series the Kinir Elite Chronicles have a very military sounding voice, each unique of course, but in some circumstances, everyone has that clipped, sharp voice of military command. (Or maybe the stealthy silent hand signals!)
YA/MG writers need to pay attention to this also! We all know that teenagers seem to have their own language. But what about teenagers in a fantasy type setting? Or from another planet? The future of our own? How would they sound then? What phrases or words would they use as slang?
Research is very helpful here, especially if your characters are military, doctors, (or some other profession requiring technical and specific phrases and words). Also looking up different cultures can lend a hand when it comes to writing an accurate voice for your characters. Looking up history (not just for historical writers) helps also. My elves and faeries in almst all my books have an air of medieval about them and the way they live. So do research all the time to learn about speech patterns and how people talked back then so my character reflect the same atmosphere.
Interviews help a lot here too! I live in the US but I have plenty of UK friends that are always too glad to help me with British slang should I need it. My Dad is military so I not only grew up with the lingo, but I can always call him up for more specific things when I need it. After you have all the lingo for a job or education level, then it comes time to decide how much of that jargon each character would use. For example, Derac, the captain of the Kinir Elite is pretty much always in Military mode. Even the way he walks/stands suggests this, but that's a different topic for another day!
So, how do you decide how your characters talk? How much research do you do regarding this? Or do you just make it up depending on the story?