Watch them. How are other content creators in your niche utilizing advertising? What types of ads do they use? What are they promoting? What do they talk about repeatedly (if you keep seeing the same affiliate product show up again and again, there’s a good chance they’re making good money from it)? If you see a product or service they talk about that jogs your memory and you can ethically promote it too, find affiliate information by the methods described above.
While I was doing WordPress speed optimization I noticed lots of people needed it, but very few people supplied it (there were a lack of services and tutorials when I researched Google). I also knew hosting was the #1 factor of website speed factor and these companies paid up to $200/sale. Hosting is a competitive space but the commissions and lack of supply enticed me.
If you would like to take a more subtle approach, include a product or service from your company that relates into your blog post. For example, let’s say that you are a wine connoisseur and that is what your blog is based around. In any post that is enticing your readers to open up a good bottle of Merlot or what have you, it would be wise to embed an ad for a quality, easy-to-use wine opener, wine glasses or stoppers that keep the wine fresh.
Learn how it works. An affiliate marketer embeds her own unique affiliate link in her web page or blog. This link does not have any impact on customers, and it does not alter the price of any products/services being offered by affiliates. However, any time the customer makes a purchase after clicking an affiliate link within a specified time frame, the marketer gets a commission from that sale. How much you earn will depend on each affiliate's prices, commission percentages, and the number of sales you're able to initiate on a weekly or monthly basis.
Once you have a great product you believe and a target market, you'll need to stock a site with quality content that will help drive traffic and affiliate sales. This article has some great tips on the nitty gritty of creating your own website. Once you have your website set up, you'll want to optimized it for conversions and sales. Learn about the four qualities of an effective website.