I have had a lot of success making money online by writing reviews for products with affiliate programs. These pages are the probably the most common copy used for promoting products.
Make it Easy for the Visitor
Reviews are an easy way to save the visitor time comparing products that propose to solve the problem they are having by listing the positives and negatives of each one. You want to make sure you list all of the information that the person will be looking for when making a purchase decision. Make it clear to them how each product can help them solve their problem whether it be to save them money, time, or increase their overall happiness. If they read your review and still have questions, they are going to go looking for answers somewhere else without having clicked through your affiliate links.
You have to grab their attention with the headline. The best way to do this is to put yourself in their shoes and describe their pain. Are you tired of feeling insecure due to acne, do you want to build muscle quickly, get rid of those extra pounds, whatever it is that your products do.
I have found that is works best giving a brief description of each product with it's positives and negatives. How well does it solve the problem? How much is the cost, customer support, and money back guarantee? Have a call of action as the last sentence of each review and at the bottom of the page itself.
Rank them in the order of the best solution to buy (actually use #1, #2). People will see right through your copy if you are just trying to push the one that offers you the highest commissions. Your analysis on why the top product is the best out there should be convincing enough that the visitor will purchase it even if it's the most expensive.
Limit the number of products on the page from between three and seven. You'll want to use the most common products in the niche, but you can also add a few of the lesser knowns as well to differentiate yourself from other reviewers.
If you can use images next to the products you are reviewing then do it. It breaks up the text and gives the reviews a more professional look. Just remember to link to the site from all images using your affiliate link.
In order to write the highest converting review page possible you are going to have to test any change you make. The metrics that you will have to monitor are your overall traffic to the review page and then how many people purchase after going to that page.
If you are using advertising to drive traffic to the page you will be testing changes in your advertisements in order to increase the number of people to the page. If you are testing conversion rates, you want to see how changes you make on the actual page increase or decrease the percentage of people that purchase after coming to your page.
Your goal when writing product reviews is to convert your visitors to buyers. You have to motivate people to purchase one of the products and to click through your link to do so.