A 404 error page isn’t necessarily a bad thing – if you do it the right way – but here’s another suggestion from Vivek on how to utilise these pages and to see what your visitors are doing on them.
“A great call to action (CTA) on your 404 pages is a must to ensure the user experience (UX) isn’t negatively impacted when they encounter such a page. As part of your 404 page/CTA you could also include a search field and track what your visitors are searching for once they encounter a 404.
By adding a search field and tracking search terms in your analytics, you can see how visitors react to the 404 pages and what they then search for – this can lead to insights as to which pages you could, or should, make more prominent or discoverable both on-site and via SERP.
By ensuring your site and 404 pages are tagged correctly, you can also capture the incorrect URL that lead to the 404 within your analytics. Again, this can offer insights in to how to improve the site structure and navigation, as well as even how your URLs are structured – you could find that people are being taken to a 404 due to a miss-spelled URL or one that’s hard to read and type correctly.”