The following is a list of questions you can ask yourself to help you consider what you will be taking into account for the story project you are creating. They aren't necesserily thorough, but thry will get you thinking.
There are two colloquial terms used within creative writing communities are pantser and planner, the former being someone who writes their story by the seat of their pants, just letting the story take them where they need with minimal planning or outline. The latter is rather self explanatory, a planner is someone who plans their story rather efficiantly, with proper outines for each section and arc of the story. I'd say most people find a balance between the two, and its better to just try things out and see what works best for you.
Every revelvant character has an arc for the most part, very few main characters remain static for the entire story. When considering your character you want to figure out how their arc will play into the story, how do their relationships, personality, and/or values change? Reminder the arc they go through doesn't have to be a positive one, it could be about change, but it could just as well be about regression.