Good Morning/Afternoon or Evening!
One of the most important processes in writing a novel, novella or short story is knowing your characters. Make them real. You don’t have to give all the information to the readers but the more you know about them the more rounded they will become.
I find that one of the easiest ways to create a character is to interview them. Yes, I’m aware that sounds mental, but lets face it, you’re a writer so this is by far not the maddest thing you do! For me, asking them lots of questions gives me an insight into who they are but also stops me from making the characters too similar, or worse still, too boring.
My advice to you is to sit down with them (outside if you like, go mad, why not!) and get to know them in depth. It will make a difference to your writing, I’m sure.
Here is a rather handy questionnaire for you to use as you please.