Find what you love, base your income on that after making sure it's profitable too.
Try spyfu.com for keyword research, you're looking for something with at least 1000 monthly searches and close to $1 Cost-Per-Click (all this is important when using Adsense)
Post content of the niche you found, make it your own of course. And host Adsense ads on your blog. After that, just promote it on Youtube and Social Media (Facebook, etc.) and regularly update it.
You can let it grow from there. Depending on your niche, you could get 3-5 blogs and make roughly $10 a day, that's up to you.