I meet quite a lot of people who want a career change but just aren't sure what else they could do. To be honest I felt the same as a teacher/librarian; education was all I'd really felt good at, but sadly I just no longer felt challenged by it.
I started by considering what it was I was unhappy with in my current role. I figured there was little point in giving up a good career if I ended up hating the same things in another job. I isolated the elements of the role that I was unhappy with, as well as the elements I loved about it.
This left me with a precise list of things I would like to find in my new career choice, and minimised the risk of giving up something good, for something less so.
Next it was time to reflect on what I was best at, as well as what I was not so good at. It makes sense to capitalise on your strengths rather than your weaknesses! I identified the character traits that had made me a good teacher, so that I could make sure I continued to develop and use them to my advantage. This also reassured me that my career journey up till this point hadn't be wasted - it's all part of the journey!
I tried to visualise my perfect working week. Would I prefer to work in with others or alone? Flexible hours or a nice routine? Working from home or travelling about? Making things? There really is no point starting a new business venture that includes too many tasks you don't enjoy doing!
If you're still not sure, ask people who know you. Their answers about what careers you'd be good at may well surprise you.
My one word of caution (I don't give these often): Just because you'd love to do something, doesn't mean you can earn a living doing it. Passion and desire sadly aren't enough on their own! The next step is research and identify a niche. Keep an open mind, and you'll find it.