As a Seller:
Clean descriptive headlines.
A body section that gives a brief overview of the product features and uses.
Images, more than one angle, preferring the front, back, and side.
Detailed product specifics ie: weight, size, and ingredients.
Customer feedback and reviews.
A means to share the product listing socially.
This is all the info needed to sell through ads or
affiliate marketingas long as you have done this job correctly.
For Affiliates:
You should have a blog on your own domain name. A free blog is not a permanent home and can be closed by the blog host for any and/or no reason given at any time.
On the blog write a thorough review of the product. Share images, list a more in-depth description of how and who benefits from its use. Share things like pricing, shipping info and tested and product specs.
Be sure to have a means of social media sharing on your blog, a subscription form to follow up or send other product listings and updates, and have social media profiles to share the review to as well.
Be sure to set the 5 social signals for search in the infographic below.

Advertise the review using a mixture of free and paid media with a heavy focus on sales forums, safe e-mails, search engine marketing, and classifieds listings.
The biggest pitfall comes from not training your brain for a task at hand. If you are a seller and don't know how to write ad copy, hire a copywriter or take a class first.
Try not to use a free blog. These don't index well in search, they look less professional than a me.com domain, and you could get buried by having your site shut down as SPAM if they think your reviews are more advertising than a review.