The best way to find an answer to your question is to start doing some thorough research. I would suggest that you start by searching trending keywords and phrases that have high monthly search volume but that aren't so competitive at the same time. Then, you can move on to analyzing some big niches to see the situation and competitiveness there, and when you find some that aren't too saturated and that have a chance for progress, you should start thinking about micro-niches, or their subcategories about which you could orient your blog articles about, and you should also pay attention to the level of knowledge that you have about some topics.