You’ve probably heard of this tool, but may not know how beneficial it is. The cost is very low if you’re running any sort of volume through your website with search engine traffic, whether with SEO or PPC. Try SEMRush Free!
With a high accuracy, SEMRush tells you the keywords your competitor is ranked on, and what pages they’re ranking for. It will help you fill in giant holes in your content. Even if you have great coverage as a website, the incremental value of scoping out your competitors will help you truly dominate.
They aren’t always accurate on the search volume for those keywords, but nonetheless are invaluable for knowing what your competitor’s “pie” looks like and where there are giant holes in your marketing plan.