Linking back and forth between different pages on your site produces a statistically significant improvement in search rankings.
(And not just for the pages on the receiving end, but surprisingly also for the pages that are doing the linking.)
Here are two good rules of thumb for internal linking:
#1: Try to link from each piece of content to at least 3-5+ other pieces of content on your site. (Assuming you can do it in a natural way.)
#2: Use anchor text based on the main keyword that the target page is trying to rank for.
For example, I’d like my article on content marketing tips to rank higher for the keyword “content marketing tips”. So in the preceding sentence just now, I linked to it using that phrase as the anchor text.
Note: this means you should not only add internal links from each new piece of content you publish… but also go back and add internal links from older content to your newer work.