3 years ago, I asked for help around how to get revenue from a website with decent traffic (https://news.ycombinator.com/item?id=5342144). I got some really good feedbacks but didn't action them. My main issue was that I wanted to get revenue while keeping most of the content free.

In November, I finally managed to push out a subscription based system that provides extra-content (videos), online access to exercises and the ability to get certificates of completion: https://pentesterlab.com/pro. The growth is steady so far and people love the service.