I have three methods that I use:
1) I will pose a question in a FB group, or a bloggers network, asking “what’s your #1 problem with X?” And then based on the responses, I’ll write a post answering how I would solve that problem.
2) I’ll pick a topic that I know a lot about and try to apply that knowledge to ANOTHER topic in a new and interesting way (I.e., my post on elevator pitches)
3) I’ll pick a topic I know next to nothing about, but am really interested in learning more about. This is my “the best way to learn something is to teach it” method.