Writing content without diluting the relevancy or authority of existing pages

Hi! I`m really interested in how to write fresh content without diluting the relevancy or authority of existing pages. For example...

Let’s say I have a page of content that is the absolute authority for a given keyword; it ranks #1 and I always want it to come up in SERPs.

If fresh content updates in the form of new pages are required to remain competitive, how can the original page stay the most relevant and visible in searches?