Personally, I prefer social media traffic to other sources because it’s quick (you don’t necessarily need a large following) and quite warm.
YouTube, on the other hand, is a lot more “residual”. Unlike facebook or instagram for instance, the platform sticks longer because of its algorithm and news feed, just the way it is designed.
There is a good guide on theaffiliatemonkey site entitled “Effective Affiliate Marketing: How Do I Promote My Affiliate Link” that you can view.
Link – https://theaffiliatemonkey.com/effective-affiliate-marketing-how-do-i-promote-my-affiliate-link/
There are other ways to get free traffic, such as blogging and guest posts, podcasts, twitter, reddit, and forums.