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.
Take advantage of marketing tools whenever possible. Many affiliate programs offer useful resources to their affiliates aimed at helping affiliates make more sales. These range from monthly newsletters highlighting upcoming sales, tips or affiliate case studies, Facebook Groups just for affiliates, private webinars explaining marketing strategies in depth and more. Ultimate Bundles does this exceptionally well.