I would wait to do an serious marketing of your channel. Promotion via social media at your current stage is fine, but if you're going to pay to advertise or try to hit various forums, I'd wait until your channel has more videos and a consistent schedule before you invest a major amount of time.
There's two main reasons to wait on promoting your channel. When you're first starting off, your quality may not be quite where you want it to be. Obviously you're always going to improve as you make more videos, but if your channel isn't up to par, promoting it to the masses is just going to show more people that your channel is lacking. Let's say that your three videos are really good. The other reason you don't want to promote too early is lack of content. If I'm interested in your channel from watching one video, I'll click over to your channel and watch a few more. I might even subscribe, but the problem here is that I've watched everything you have to offer. Unless you show up in my sub feed, there's no reason to ever come back to your channel since I've already seen everything.
