I know subscriptions are a litttttlleeee controversial but hear me out: bloggers like ElephantJournal have been super successful using Wall Street Journals approach of providing 3-5 posts a month for free and then asking for a small subscription fee. This one is worth thoroughly A/B testing though, because if it impacts your session depth and overall pageviews, your display ad revenue will take a hit.
“Let me remind you again that when you put a book out there, you are a published author in a space where you are an expert. Your book becomes the ultimate business card, not to mention a source of ongoing revenue. Did someone say “ongoing revenue?”. Who does not need to make some extra money on a regular basis? Realize that this book will take some work to complete once, but thereafter it exists forever – working to bring you royalty checks five, ten, twenty years from now. Money will be consistently flowing into your bank account. If you write a good book that provides real value, then you realistically have a revenue stream which will bring income for decades to come.”