@Dreamerswizz15 HI! I'm so glad you enjoyed it! I'm not sure I've ever been asked this question, but I think the best two tips I can give are to write well rounded, dimensional characters and to show, not tell.
When I'm outlining my novel, I always do a character profile for my main characters. I write down their name, age, main role in the book, and I give them whole background stories that may or may not come up in the novel.
I also give them quirks and 3-5 personality traits that I try to stay true to while I write my novel. It also really helps to write down what their internal struggles are (like anxiety) and external struggles are (like for June and Jasper that they had to get to Florida on time for the wedding).
As for showing and not telling -- I feel like descriptions really bring your novel and characters to life. For example, June has anxiety and instead of just saying she's anxious, I try to show that she is. When she's feeling uneasy, I always try to write what her hands are do -- they're either playing with a bag of marshmallows or pulling on her hair, for example. Being able to envision what your characters are doing really brings your story to life.
Not going to lie -- I'm always googling better ways to do these two things and looking for examples. I'm definitely not perfect at either of these but I feel like if we just keep practicing we'll get better!