1. You set the rules for your fictional world so this gives enormous freedom to explore ideas. The world and its characters, no matter how bizarre by Earth standards, still have to make sense and there should be good reasons for them being/acting the way they are/do but other than that, away you go!
2. You can explore different aspects of character via different "stars" of your work.
3. You can develop your characters over time and many books. Sam Vimes in Terry Pratchett's Discworld series is a great example of how this works when brilliantly done. There must be enough scope in your character for that person to want to change bad things, improve good things about them and so on. Interviewing your characters so you explore their hidden depths can be really helpful here. It can help you discover just what you do know about them before you write about them.
4. Creating characters and worlds can help give you blog post ideas too!
5. You can take what you know of life, people etc and bring those into your stories. What you don't know can usually be researched.