Harry Potter series: a great example of character development.
Let me start by saying I am no expert. I won't ever claim to be. All that I write in this "blog" will always be open to interpretation. As writers, we can bend the rules, and I encourage doing so! With that said, I want to discuss characters, you know, those people who make your story's plot worth reading.
I have a friend who nearly wrote an entire book at some 400 pages. He quite because he felt that his plot was too unoriginal and that his characters lacked, well, character. So how do you make characters worth reading? You make them like people because they are people.
Every one is different, different body types, expressions, personalities, quirks. Your characters should have the same diversity. Take inspiration from the people around you to bring your characters to life. I'm not ashamed in admitting many of my characters are based loosely off of my friends (my friends are out of this world crazy, so naturally they made good templates). As writers, we create imaginative and complex worlds, but even the smallest details have a basis in our reality.
Of course, it is always easier said than done. Characters, especially main characters, must have agency (fortitude, dreams, goals, etc. the stuff that makes us who we are). Without agency, characters become walking sacks of potatoes, and nobody likes to read about potatoes. Give your characters dreams and goals. Give your characters pasts and futures. Make each one a part of the plot, and a changing force of the plot, and you may be surprised at how real they become.
Now, I can't discuss characters without talking about one of my favorite character topics, cliches! I love them! Not only because so many character cliches are funny, overdone, or just plain boring, but also because many of them, if done right, can still make an engaging story. If you tried to avoid every cliche, you may find yourself somewhat at a loss, so as a writer of course you can take a few and twist them, just don't go overboard with them. If you feel your story has a cliche (like a farm boy realizing he has great powers and rises to prominence, or a damsel in distress that requires rescue from a dragon), make sure that you pump new life into it and make it a fresh story for the reader. George R. R. Martin is a great example of an author who takes classic fantasy tropes and dashes them against the rocks, sometimes literally.
I would love to talk more, but this post would become a book. Below, I've included several links to websites that may push you in the right direction on character development as well as lists of character cliches.
As always, thanks for reading!