I use SEMRush for keyword research (and digital competitive analysis). The first thing you want to look for is search volume: How many searches per month? Then keyword difficulty: How hard will it be to even rank for this keyword? If your "main" keyword has a high keyword difficulty, are there related keywords that are easier to rank for? Look for semantically related keywords to get an idea of sub-topics/additional posts. Look at who is ranking for the terms you want to rank for. What are they doing? What are they talking about? How can you add value through your own content?