The mechanics are ordinary. List every page, with its traffic, its enquiries if you can attribute them, when it was last updated, and whether the information is still correct. Most of that comes from your analytics and your search console in an hour. The list itself frequently produces the first finding, which is that pages exist you had forgotten publishing.
Then sort each into one of four actions rather than reading them one by one. Keep, meaning it works and needs nothing. Update, meaning the topic is still right and the content has aged. Consolidate, meaning two or three thin pages on overlapping topics should become one substantial page. Or remove, meaning it produces nothing and is no longer accurate.
Consolidation is usually where the largest gain sits and it is the least intuitive action. Three short pages competing for similar terms will each rank poorly, while one combined page carrying the strength of all three can rank well. When you merge, redirect the old addresses to the new one rather than deleting them, so whatever they accumulated transfers rather than being discarded.
Removal deserves care for the same reason. A page with no traffic may still have links pointing at it from elsewhere, and deleting it without a redirect turns those into errors. Check before removing, and redirect to the closest equivalent rather than to your home page.
Do it annually rather than continuously, and treat the output as a short list of actions rather than a report. The common failure is producing a comprehensive spreadsheet that nobody acts on, which consumes the afternoon and changes nothing. Five pages updated and three consolidated is a successful audit regardless of how many were reviewed.
Check the pages that already produce enquiries before touching anything else, and be conservative with them. The instinct during an audit is to improve everything, and rewriting a page that is currently working is the one action with genuine downside. If a page produces business, the correct treatment is usually to correct anything factually stale and leave the rest alone, saving the effort for pages that produce nothing.