We audit a lot of websites that are, by their owner's description, "not ranking". Almost none of them have a content problem. They have a crawlability problem, and it is nearly always one of the same five issues.
1. Your content does not exist until JavaScript runs
If your site is a client-rendered single-page application, the HTML a crawler receives is an empty div. Google will eventually render JavaScript, but it is a second, slower, lower-priority queue — and other crawlers do not bother at all.
Check it yourself: view source on your most important page. If you cannot find your own headline in the raw HTML, that is your problem. Server-side rendering solves this outright.
2. No structured data
Structured data is how you tell Google what a page is rather than making it infer. An article with valid BlogPosting markup is eligible for a rich result. A job posting with JobPosting markup is eligible for Google Jobs — an entire surface most companies never appear on simply because nobody added twenty lines of JSON-LD.
3. A sitemap that lies
A static sitemap.xml written once and never updated is worse than none. It sends crawlers to pages that no longer exist and omits everything published since. Generate it from your database so it is correct by construction.
4. Slug changes with no redirects
Rename a URL and you throw away every bit of ranking that URL had earned, plus every inbound link pointing at it. A 301 redirect preserves both. This should be automatic in your CMS, not a task someone remembers.
5. Core Web Vitals nobody measured
Page experience is a real ranking signal, and more importantly a real conversion signal. The usual culprits are unoptimised images, render-blocking fonts and layout shift from elements without reserved dimensions. All three are solvable in an afternoon.
Where to start
Run your most valuable page through Google's Rich Results Test and PageSpeed Insights. Between them they will identify most of the above in about five minutes. Fix the crawlability issues before you spend anything on content — content nobody can crawl earns nothing.