Always fill out the comment box to “sell” your platform. If you are given the opportunity to explain why you are interested in a program, do it! Use the space to highlight why you would be an asset to the program. Talk about how your audience is their audience. Talk about the size of your mailing list (if it’s significant). Talk about your success with similar programs. Talk about where and how you will promote (hopefully you’ve done a bit of research so you know what they’re hoping for). Don’t sound desperate and certainly don’t lie about anything, but be upfront and honest about how this will be a win for them.
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.
Before jumping into starting an affiliate marketing business, learn all that's involved in making it a success. More importantly, if you decide to pursue an affiliate marketing business, or want to add affiliate marketing to an existing business, understand that it's not fast, automatic, nor without effort. Like all home businesses, you need a plan and daily involvement to make money with an online affiliate marketing.
While these models have diminished in mature e-commerce and online advertising markets they are still prevalent in some more nascent industries. China is one example where Affiliate Marketing does not overtly resemble the same model in the West. With many affiliates being paid a flat "Cost Per Day" with some networks offering Cost Per Click or CPM.