Ok, I really geek out when it comes to marketing (its my current 9-5), so this post was a lot longer than anticipated, however I think there is a ton of useful info.
I've actually been speaking to a number of artist friends who have asked me the same question.
Here is a bunch of things I have found work through my own experience, and also talking to other successful artists.
Based on what you want to achieve (selling prints), you need to ask yourself "Where are my target audience hanging out and engaging in work similar to mine?"
Quick overview of the popular methods of promotion online
To cut to the chase, my experience and through speaking with other artists is that Twitter isn’t the best platform for artists to promote their work. There is too much noise and the people on there aren’t as engaged as they are on other platforms.
In regards to Facebook, it can be a hit and miss for artists. It depends on your audience, and how they interact with similar art to yours. Often the case, promoting your art on Facebook is a “pay to play” situation.
I wouldn’t bother with SEO at first until you start to make a name for yourself and people are searching for you online.
Instagram, in general, is one of the better places for artists to promote their work, and eventually guide people to your website where they can buy stuff. It is orientated to the visually minded, which is what your audience will be. Its based on developing relationships, which is also what helps artists sell a piece.
There are plenty of other platforms and social media sites out there that could help. But I guess it comes down to which one.
How to choose
There are so many options out there. Already you are off to a good start by knowing what you want to do – sell prints online.
However, you probably don't know where to start. Here's how you can find out no matter what art style you have.
The next step is to find artists who have similar styles to you and are successful online.
Once you have found these artists see what they are doing that is working. Look at their overall marketing strategy, and take note of what they are doing in each post. If you do this for a number of successful artists you will start to see patterns that you can take on and try yourself.
To expand on this, contact the artist directly and ask if you can have a quick chat with them. You can ask them questions about what works, and what you should avoid. Again, you will gain a lot more clarity about what you should do and what should work.
The mindset you should take on
After doing the above, you will have a very clear idea what you want to do and how you should go about it. AND you will still have a 100 more questions as a result.
The trick here is to take on the mindset of experimenting. You are never going to have a marketing plan perfect the first time. I’ve been marketing for 10 years, and I never get a marketing plan perfect the first time (if I do, I wonder what is wrong that I’m not seeing). The key is to experiment.
For example, let's say you have chosen to promote yourself via instagram. You know this hashtag thing works, but you are not sure which hashtags are best. The solution: choose the top 20-25 you think will work and use them for a set period of time - lets say 2 weeks if you post daily. At the end of those two weeks, look at how you went. Then, change 5 or so of those hashtags, and use that new combination for two weeks. You can compare which combinations of hashtags got better results for you. By continually and systematically experimenting, you will refine the effectiveness of the hashtags you use.
Another example of experimenting on Instagram: Test different types of content to see what engagement you get. You can try a direct front-on photo of your piece. You might also try a photo of your piece on your desk, surrounded by the mediums you used to create it. You might put up a time lapse of you creating the piece. Try them all and take note of what works, and what doesn’t. Don’t be afraid to include works in progress. It tells a story….which brings me to my next point.
Its not the art (on its own) that sells, it’s the relationship that the customer has to the piece
Building relationships with your customers is what sells art. This is why “buying followers” doesn’t work – they are either bots, or not that engaged.
So how do you build a relationship with your audience? Through stories. Creating a new piece? Take photos as you go, documenting the process and your experience creating it. Have two character designs that you love but can’t pick which one to use? Throw it to your audience and conduct a poll.
By telling a story and encourage follower interaction, your art becomes something that the audience becomes invested into. In some small way, its their journey too. When it comes time for you to sell this art, they want to have a memento of this journey. They love it more, because it's not just a picture, it’s the hours you put into it, the love and precision. The story behind it. It’s also the input that they may have had in the process too.
So that should give you a massive amount of insights, and hopefully actions you can take to refine what you should do to get a ton of engaged followers.
My last point is it takes time. Promoting yourself online, particularly in social, is a marathon, not a sprint. Online marketing is like a heavy fly wheel. At the start it takes a lot of effort to get any movement, however if you are consistant and smart in your effort, the fly wheel will move faster and faster and gain momentum. It will eventually get to a point where to keep up the momentum, the effort involved is minute, however it will take a while to get there.
I have a ton of more tactical stuff, but as an overall strategy, the above will see you go far.