Thanks for sharing these tips, Brian. Agree with all of these, except maybe #3 Delete zombie pages. A better strategy would be to update these pages with fresh content and convert them into a long form blog posts/guides. Deleting them entirely would mean either setting up a 404 or 301 redirect – both of which can hurt your organic traffic in the short run.
Google updates its search algorithm frequently. For example, on February 23rd, 2016, Google made significant changes to AdWords, removing right-column ads entirely and rolling out 4-ad top blocks on many commercial searches. While this was a paid search update, it had significant implications for CTR for both paid and organic results, especially on competitive keywords.
Organic search results are free and display below Google Ads and sometimes local results. Google uses a sophisticated algorithm to determine which sites rank highest for organic search results based on keyword usage, relevance, site design, and other factors. Generally, Google provides the highest quality, most relevant results based on the keyword(s) used by the searcher.