I experimented with a collab idea around 800 subs with @Furry Gurus. Not exactly sure how much it helped her channel, but the video on my channel has gotten about 1,200 views so far. The idea was to have my Dalmatian barking at her dog/cat videos and feature the links to her channel and videos that are playing as an annotation. I also put my buddy's band's music in some of my videos, I always link back to their song or web page. That basically gives me awesome music that is royalty free, and it possibly steers traffic to them. You need to find something that will help the other person and yourself. In each case for me, it added value to my videos and could possibly steer traffic to the other people so everyone wins.
Here's an example to show you how simple it was. We are in different countries too, so you don't even have to be on the same continent if you are creative. I just remembered I also did a flame throwing dog video lol, I basically linked to their videos in my description.
