Books. For a writer, producing a manuscript is just the first step. If you want it to sell, you should get feedback on it from other writers – preferably successful ones – and go through multiple rounds of editing to turn it into a professional-quality work. You could even consider hiring an editor to whip your manuscript into shape, particularly if you have trouble with mechanics such as grammar and punctuation. Then you need to either use some page layout software to turn your manuscript into a readable book, or otherwise hire a professional to do it for you.
While all the ideas in this article can and do work, you can’t go in half cocked. Just putting up a niche website and expecting people to magically come and click on your ads won’t get you very far. Instead, you’ll need to put work into building an audience. You can put a course up on Udemy in a few hours, or a theme on ThemeForest, but unless you market it, you won’t sell very many copies. 

Although this article has been written in 2007, now in Feb 2014, I still find it full of great advice and tips. What I learned from this article is that when writing a review I should focus on how this product helped me achieve X instead of simply repeating and enforcing the features and benefits of the product that can also be found on the sales page.