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.
The best way to find suitable brands to promote is by simply using a search engine using: '[Brand] + Affiliate Program'. Some companies run in-house affiliate programs however, this is a very specialist area. Therefore, most companies opt to employ an 'affiliate network' which has already built a large base of affiliates and gained years of experience in running successful programs for clients.
Do you have zero interest in an expensive mountain bike the company you are an affiliate of sells? Well, you probably don’t want to feature it on your blog, as it is extremely difficult to persuade readers (or anyone for that matter) that they should buy something you wouldn’t be caught spending a single penny on. When you are passionate about a product or–at the very least–interested in learning more about it, this will come through to your readers, engage them and better coax them to buy
Affiliate marketing is also called "performance marketing", in reference to how sales employees are typically being compensated. Such employees are typically paid a commission for each sale they close, and sometimes are paid performance incentives for exceeding objectives. Affiliates are not employed by the advertiser whose products or services they promote, but the compensation models applied to affiliate marketing are very similar to the ones used for people in the advertisers' internal sales department.