First, you need to connect in as many ways as possible with the public which means you need a profile on as many social media sites as you can get on and still manage! You need a website! Even if it is just a free weebly site or a blogger blog, you need a place to serve as your home base and hub to link all of your other online places together. On this website or blog you need to post links to all the other places that you and your art can be found. Social media buttons are perfect for this but are not available for every site so you might have to get creative making your own buttons or just using text links.
I am on Instagram and have been since before I started selling my art, so I already had a lot of friends (followers) there but I actually don't use instagram to promote that much, partly because it isn't well received and partly because there is no way to embed links into your posts. So I just have a link to my website in my bio and once in awhile I will post a promotional photo of a new product or something that just sold.
The next place that I don't use much to promote my work is Facebook although I have heard that other people have success doing so. Self promo on Facebook is tricky because you don't want to bombard your friends and family with posts trying to sell your art unless you want them to unfriend you. I mean once in awhile if you think someone will share your post ok but don't go overboard on your own timeline. Instead create a Facebook page to display your best work (like a gallery) and link it to your site (if you have a store there) or to your POD site where they can buy a piece that they like and see more of your work. Another way to use Facebook to promote is to join groups that allow you to post your links but you still need to post sparingly (two or three a day, more than that is usually considered too much). This is a good way to keep from spamming your friends!
Twitter is another place you can use but with the same limitations, don't post too many promos at one time and try to mix it up with some other content and one more tip which is good for all the sites you use, promote other people too! On Twitter retweeting is a huge thing even though I am new to the Twitter-sphere I can already tell that retweeting is a good way to get noticed and get your own tweets retweeted. I'll go into more detail about twitter on a later post after I learn more about how it works.
My go to social media for promotions is Google+! Yep, I said Google+. If you are not using G+ you are missing a great way to get your art seen. The best thing about G+ is that many business people and entrepreneurs use it and promoting is not frowned upon as much as other sites. There are many communities (groups) you can join that are niches some especially for advertising and promotions. If you join enough different groups you can promote things all day long without posting to the same group twice and you reach a different audience each time! Resharing is common and encouraged. G+ also has a collections feature which I have used to create public collections that anyone who is interested in my topic can follow. One of my collections is especially for promoting products from Zazzle. I share my own products and other Zazzler's as well. And I find that in G+ Communites, members are usually very active and engaged. One tip when adding people to your circles, check their profile and see when their last post was and don't add anybody who hasn't posted for over a year. They probably won't be back... or active. They probably never got the hang of G+ or they didn't like it and so they gave up. I have found several inactive accounts in the find people section that are still open but no new posts for months or even years and you want to connect with people, so avoid these dead accounts. Also, I notice when I post to the public in general, I get a lot less interaction than when I post to certain of my groups. But the main advantage of posting your products or art to G+ is that helps you get found by Google search engine much better! I don't know if it is because they search their own connections first or what, but it definitely helps.
Next on my top places to promote is Pinterest. And it works much the same as Google plus. You need to make lots of boards, follow lots of people and join group boards, especially boards that are relevant to what you promote. I belong to art boards, zazzle product boards, general product and shopping boards, no limit pinning and pin anything boards etc... This allows me to pin as much as I want each day without pinning to the same board more than twice a day. Keep building your Pinterest presence even if you are not getting much response because eventually people will start saving your pins and this increases your audience exponentially, along with the chance of making a sale.
I also post to Wanelo and Polyvore but other than helping get me seen by search engines I can't really say they have much impact on my traffic or sales. I recently made a blogger blog for me and my fellow Zazzlers to auto post by email our Zazzle collections and I advertised it in the Zazzle forum and have a few of my affiliate links posted on it because every little bit counts. And I have been exploring and researching other ways to drive traffic which I will write about more later. In closing I just want to re-emphasize the importance of promoting other artists as well as yourself. This opens up interaction with other artists , gets people talking and draws attention to your own work and is just the courteous thing to do even if you are not going to make a commission for it. So as you can see there is an art to self promotion and one key thing to remember is it is not all about you.
I have learned recently about a very popular software solution that can help anybody start selling from anywhere, and get your store set up in 60 seconds with many valuable business tools to help you be successful with your online store. It is called Shopify and you can try it free for 14 days.
(Disclosure: I am a Shopify Affiliate and make commissions from any sales generated by my links)