In Neil Gaiman's MasterClass series on storytelling, he says that he discovers his characters by how they express themselves, the way they talk, the words they use or don't use. It's the way he gets to know his characters first. So just listening to people talking out in the world and writing down phrases or sentences to get you in the groove of writing dialogue might be helpful.

The following are a few things about dialogue copied directly from the MasterClass Classguide to "Neil Gaiman Teaches the Art of Storytelling," p. 44.
• Fine-tune your language by using select sentence fragments—“Sounds great” is more natural than “That sounds great.”
• Use contractions when possible—“We’ll go together” is more comfortable than “We will go together.”
• Trim excess filler words, like “uh” and “well.”
• Remember it’s unusual for people to call each other by name, so police those areas where your characters call each other by name.
• Also, not everything has to be verbal—body language is a real-life communication tool. Instead of having your character shout, “I hate you!” show them kick a chair.

I wish I'd thought to reread the whole classguide over the summer!
           
     “Judge tenderly, if you must. There is usually a side you have not heard,
     a story you know nothing about, and a battle waged that you do not have to fight.”                     ~Traci Lea Larussa