Keeping at it is my best advice. When people say to befriend YouTube creators, it's not an immediate, "Hi, I make YouTube videos so come check out my channel," which I see a lot of. I tend to comment on people's videos for a long time before even mentioning I have a channel, and they usually find out on their own after enough comments. it
There's also many types of social media (Twitter, Facebook, Instagram, Pinterest, Snapchat, etc.) to promote from. And forums like this one and Reddit and YouTube forums and Google+ forums, etc. I also publish all my videos on my personal blog.
It takes a lot of time and effort and can feel like you're making no progress at all sometimes, but eventually, you make progress. The main thing is to not give up before it starts to take hold. I see that a lot from new creators who expect to have lots and lots of success after 3-4 months.