Who is in your target market? - SEO today is not about just grabbing as much traffic as possible, but instead attracting high-value visitors interested in what you offer. In terms of demographics, what is your market searching for? How are they performing web searches? Where are they located? The more specific your answers, the more valuable your investments in SEO become. Google Analytics is a good place to start your investigations!
I was used to work with Tools like Sistrix, Ahrefs or Searchmetrics and did not know about SE Ranking before. But those tools were too cost-intensive for a small and quick start into SEO so I tried it out and I am quite satisfied with it. I like the ability to pay for certain services with credits, as I am not using them on a very frequent level, so it actually gives me greater flexibility to only use them when needed and not paying for them even when not using them.