Internal linking is treated like a checkbox: yes, we do internal linking. But the question is not whether you do it. The question is whether you are doing it well enough that the link equity from your strongest pages is reaching your most valuable target pages.
The 30-minute audit
Identify your three highest-traffic pages. Identify your three highest-revenue pages. If those two lists do not overlap, ask yourself how many internal links connect the first list to the second. Often the answer is zero.
Add three relevant, in-context links from each high-traffic page to each high-revenue page. Wait three weeks. Re-check rankings.