Always make affiliate links nofollow. Google’s goal is to provide its users with the best possible search results to their search queries. One of the main ways they figure out which webpages are the best is through links. The Google bots crawl the web, reading text. When they come to a link, it’s like an open door. They follow the link (walk through the door) and explore the site you linked to.
Don’t exhaust all the information about the product with your link. Offer enough information to your readers so they know what the link is, but I don’t recommend giving too much detail on your own site for a two reasons. First, product information, like price, often changes. If you mention the price on your site and someone clicks over and finds a different price, it’s confusing. Second, many times, the product details and features are better explained by the makers of the product. It’s best to stick to your own experience on your site.
Contact the company directly. If you use a product or service and want to recommend it but you can’t find evidence of an affiliate program, consider approaching them and asking if they are willing to set one up (maybe with your help). Highlight your audience and the value of your recommendation. Explain that an affiliate program is simply rewarding happy customers (you!) for promoting, and they don’t have to pay until a sale is made.
When promoting affiliate offers, just make sure you are fully aware of all the terms and conditions attached to your affiliate program. Some programs can be strict about how they allow you to promote their products. For example, some may limit you to banner ads and links only, while others will allow you to use paid advertising, but won't allow email marketing.