Find a profitable niche. Starting with your interests, write down as many niche ideas as you can. Think about topics people might search online. Ideas include passions (like surfing or body building), fears (like spiders or speaking in front of crowds) and problems (like getting out of debt). Do keyword research to see it others are interested in the topic. Find out if a domain name is available that matches the keyword 100 percent. 
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.
If my piece of content is so unique and valuable around hiking backpack recommendations, that other reputable outdoor websites are willing to link to it and build the page’s authority, then I’d have a very real opportunity to rank high in organic search for these search terms (meaning, my page will come up first when someone searches for hiking backpacks).