How do they show stress? Do you have any “stiff upper lip” types? If so, how do they show stress? The traditional way would be a nervous tic but can you show a unique way for your unique character to reflect their state of mind?
What do your characters have? How did they develop these? Do they drive a loved one mad? Who are their loved ones? How did those relationships develop? You may well find you don’t need to put all or any of this into your story but as long as you know the answers you will be able to write about and for your characters with confidence, which will show in your stories.
Good habits? Quirks?
Do they agree with their world’s politics? Have they any ways of showing their views? What are the consequences?
Make sure you’ve got the right balance of characters in your work. Too many humorous characters or whatever tip your work. Humour always works best when shown up against something else in any case. Wodehouse’s Wooster wouldn’t be funny if he hadn’t various odious aunts to outwit. Also Wooster, whilst rightly acknowledging Jeeves as a genius, is not totally dimwitted. Ensure your characters aren’t either. Each of your creations must have something positive going for them or you won’t get reader sympathy.
Do your characters change their minds? Do they hesitate? Do they find their original purpose isn’t what they thought and they need to adjust it or need to adjust what they do? Give your characters hell! It’s fun! And makes for better writing! What’s there not to like about that?
Character Relationships Your characters should have friends and enemies. Relationships complicate plot which is all to the good as far as you’re concerned. You want your characters not to have an easy time of it!