You could start a blog where you review books or you could be a guest blogger and get paid to write about books that you read.
To make fast cash, I would surf the internet and look for blogs that post often on a topic that you like to read about.
If they don't have many book reviews, approach the owner and ask if they would be willing to pay you to write posts that review books on that topic.
Also look for blogging jobs on sites like problogger.net where you can get paid for writing.
This will give you some money now. But if you want longer-term passive income, you should think about starting a blog at some point.
Hope that helps!