Off the top of my head:
- Learn some liquid to help customize title tags, canonicals where needed.
- Figure out the seo.hidden metafield for if/when you need to no-index or remove a page from sitemap.
- Familiarize yourself with the URL structures and the duplicate page structure.
- Look into the new-ish robots.txt customization and how you can blend in liquid logic
- Form an opinion on if it’s worth flattening the site structure down to root /product/xyz URLs and removing the longer duplicate /category/abc/product/xyz URLs from being internally linked to
- Figure out how to improve SCHEMA, rip out crap low-quality microdata from a theme code, and how to integrate with 3rd party review apps. There are some pre-built scripts and decent apps out there that will do it for you - or write your own.
- Familiarize yourself with the OS2.0 theme architecture and how it can be leveraged to introduce unique/deep BTF content to each product page like additional sections, FAQs to increase topic relevance.
- Familiarize yourself with product feed apps like Google Shopping Feed and DataFeedWatch that pair well with Shopify and understand limitations of the default app. Now that Free Product Listings are a thing - optimizing them is important
- Figure out how to bulk edit - Matrixify can be extremely useful here
- You can actually use CloudFlare O2O
- Figure out multi-domain, currency pricing, i18n, hreflang tag options - there have been some new features released in the last year or so.
That’s a few things. There’s a decent article by ContentKing on Shopify SEO that looks at some of the technical aspects too.