Some of my best results have come from good internal linking. It’s so often overlooked but a good technique I often use when take on someone’s website is.

Google search console – top 10 pages for organic clicks in the last month – add links in those pages to other pages on the site I want to rank (where relevant)

This has worked for me more often than not as a starting point. For a lot of sites this is power blogs and content that outweigh the category pages.