First of all, if I want to start my brand new blog, I would pick the topic I love and curious about it. I could only keep writing if I write something I want to share. Or I might run out of idea quickly.
You can write anything, like helping people to start their own blog with WordPress like Bluchic and WPbeginner, which are good website to teach people start a blog to make money. If you want to share the scam experiences online to guide people to spot online scam, you can start your blog like Cyclonis Blog, which is a company blog but you may find something interesting about their writing.
If you just want to write something for yourself, not looking forward to any audience, then you could just ignore what I say following. If you do, then you have to consider the questions as follow.
"Are there others who are interested in the same thing?"
You could just Google it and see how many results could there be? If it only gets like 5 pages, then you might not get audience for your blog. And you could find out details to help you determine more related ideas.
"Is my idea too broad"?
Choose a specific topic. For example, if you want to start your travel blog, choose a more specific keyword like backpacking or RV travel.
If you specify your blog ideas, you might get more suggestions or ideas from others:) too.