There are various fields to write in -
1. Writing poetry is an evergreen topic.
2. Writing about sports matches is also a great idea. (if u r a sports enthusiast).
3. You may write informative articles about whatever your interests are.
4. You can also write a real life incident or experience.
5. A particular area you live in, and its info can make a wonderful hub.
A bulk of ideas can be thought of when writing a new hub. But choosing whatever you love is obvious.