Turn The 404 Error Pages
Creating 404 pages may not be at the top of your list when designing a website, but the best ones work to convey brand identity and keep visitors entertained. Of course, you ideally don’t want users to see a 404 page at all, but you can turn the situation to your advantage with a bit of thought and use those error pages as ambassadors for your brand.
Increase the number of indexed pages of your website
your website has many pages, there will be many dead links as well. How would you like to ramp up your search traffic by getting more website pages indexed via your error 404 page? I used this strategy to increase website traffic by 9% in a month. I linked out to a random 25-50 internal pages by running an algorithm.
Call to action
Remember what we said about your 404 page practically serving as a landing page? So apply some landing page logic: add in a download or signup button, or at the very least, a search box.
A search field
A search field on a 404 page design layout gives the user an opportunity to go on with searching for whatever page they had in mind thus making them remain where they are.