There are lots and lots of artists out there pursuing art and an art career. Just as there is no one way to paint, there is also no one path to a successful career as an artist. It is a journey full of growth and learning.
I come across much that is written for artists about marketing their work. I also come across the work of many artists who are marketing like crazy when perhaps they should be focusing on something else.
So here is my Number One Marketing Tip for Artists. It can be condensed down to two simple words, but here it is in full: Don't pursue success. Pursue Excellence. Then, success will likely follow.
If you strive for excellence in what you do, good things will happen and doors will open to you. Galleries will invite you in instead of the other way around. While skillful marketing is a plus with all the online opportunities artists have now, no amount of marketing will compensate for artwork that is not the very best you are capable of. As to what makes art excellent, that is a big mysterious question with many answers! If you're a realist painter, learn the drawing skills needed. If you're abstract, learn about color harmony or composition. And whatever kind of art you make, know what it is you are passionate about and make sure you're communicating that to the viewer.
Best wishes on your journey!