The secret to high art sales, which must be done IN ORDER:
craving -> creativity -> competence -> community -> conversations -> commerce
You must have a craving to produce art. As Hugh MacLeod says, "The Hunger will give you everything. And it will take from you, everything. It will cost you your life, and there's not a damn thing you can do about it." If you don't have a craving this strong, it's probably time to think about doing something else.
Nurture your craving by acting on your creativity. In other words, create.
Lack of sales frustrates many artists more than anything else. Often, a lack of sales is caused by poor marketing strategies or, simply, poor execution of those strategies. But sometimes, a lack of sales may indicate a more fundamental issue: that the artist has not yet reached a basic level of competence in their work. In other words, your art must be competent in order to sell. Think about it: Let's say you paint wildlife, and one of your potential markets is deer hunters. If you've not properly mastered depicting the anatomy of a deer, your target market will know. And your work won't sell. Or, at a more basic level, if you've not reached a level of competence in mixing and painting colors in your landscapes - people will be able to tell that something is "off". Invest the time necessary to become competent at your craft. Find people who will be honest with you (even if it hurts to hear) to critique your art. 
After achieving competence, as people discover your art, you will find folks who are interested in your creations. Let's call these people "fans." Or, in modern guru-speak, your "tribe." You're the leader of this tribe and it's up to you to be organized and keep track of who these people are. You need to have an organized contact list and an organized email list. When someone expresses interest in you or your art, you need to add them to you contact list and make them part of your community. The more you foster a feeling of belonging and exclusivity in your fans, the more successful you'll be. Community precedes conversations which precede commerce. If you are not organized about this process and are not actively leading your fans, then you don't yet truly have a community and your sales will be lackluster. 
It's been said before that "marketing is conversations" and, indeed, you should be constantly initiating conversations with your community. That's one reason email newsletters are so powerful, as your community grows, each newsletter you send goes to more people and each one should spawn replies which initiate conversations between you and your community. Of course, blogs, social networks and good old-fashioned exhibits are all other ways to spawn conversations.
If you've done all the previous steps: you're satisfying your craving by expressing your creativity. You've put in the hours to develop your "chops" and are producing competent art. You've been nurturing your community and are having regular conversations with them. If you're doing all these things, commerce should follow. And that means sales.
Remember, Sharing Art Enriches Life.
BoldBrush/FASO Founder & Art Fanatic