I've said it many times, but by far the most successful promotion method for me has just been meeting people and making friends.
People really don't like being advertised to, so unless you happen to have an extremely eye-catching product, traditional advertising methods have a very poor conversion rate. It does work, but you have to keep trying, trying, trying, until eventually someone gets curious enough to check out your work. But you have to be careful not to be too aggressive about it, because again, people hate being advertised to. It's tough!
On the other hand, if they see you as a pretty cool person, they're way more likely to check out your work because they want to support you. Every successful social media artist I can think of doesn't just share their really cool artwork, but also their personality in a way that audiences can resonate with.
tl;dr, don't push a product, push yourself.