This is one possible route - whichever topic or doubt you end up searching the internet for, make a small post about the solution. As you grow over time, start being more comprehensive about the solutions, and try to list information on the very niche topic till the periphery of human knowledge( from history of birth to bleeding edge tech in that area). Growing more over time you will start getting in-depth and at a zen blogger stage, cross-domain.

Or you could make the blog all about you. Your personal journey of how some attained knowledge in the past, you were able to apply.