I would start with the check that several members here put first, which is whether the pages are actually indexed and crawlable, because content and links cannot help a page that Google cannot find. Hetneo made a useful distinction though, since indexation on its own is only a short check, and the more telling step is to look in Search Console at whether the indexed pages are getting impressions and where they are sitting. If they are indexed but stuck in the thirties, that points to relevance and intent rather than a technical block, and that is where I would spend the next effort. Digital Crown Agency also made a point that stayed with me, about building links before fixing what a page was actually about, and I think that order matters here too. Fixing the match between the page and the search it is meant to serve, and checking that the zero traffic figure itself is accurate, as nicenic suggested, would come before any work on links, because links would only amplify a page that is still aimed at the wrong query.