Just search for articles about monetization... or read any/all of Dan Kennedy's books.
Looks at what's currently working, like selling Ads.
Likely best to start by reading all of Bob Lotich's books, in published date sequence. If you're a fast reader, you might get through all of them in a single day.
Bob's approach to... how to say this... discovering the most lucrative Native Ads to run onsite... is worth it's weight in gold.
If you're still stuck after all this, hire someone to help you design a monetization strategy.