What's the most important thing needed to become a successful artist outside of raw talent?
Well, first… raw talent is not even remotely an important factor. The single most important thing needed to become a successful artist is to have a unique gimmick.
Maybe you cover things in diamonds, maybe you make shapes out of faces, maybe you cover all your eyes in butterflies, maybe everything you do has the exact same color palette every time, maybe you only paint really sexual things, maybe you draw squiggly lines randomly as “design-elements”, maybe everything you do looks like a propaganda poster, maybe everyone you draw has a skull head… if your work doesn’t look like it all came from the exact same place, how will people know it’s yours? You must limit your creativity so that everything you make appears as though it is your artistic essence or style. Never mind that creativity rarely trickles out in an organized fashion, but rather in an explosion of chaos and disorder… if you want to be successful—you must fight that and make your art branded and uniform.
Wait wait WAIT… that can’t be right….
Pursue greatness, subject yourself to mass criticism, accept said criticism, get better, don’t do cocaine, be a decent human being, waste less time, and never, EVER, EVER, stop doing it because you love it. As an artist, you should always be able to make whatever the fuck YOU want to make, however the fuck you want to, and if your struggle is a great one, at least you won’t have lost sight of why you do it to begin with. This is a field for the passionate—not everything you make will inspire you, but never get to a point where you are unable to love what you do because you found a sellable gimmick, grasped hold of it, and were unable to sell anything else.
You don’t need to feel some profound emotional attachment and need of expression to succeed as or even be an artist, but you do need to love what you do to the point where it ebbs and flows in tune with you. You will go through phases and changes, let your work do the same and people will notice.
tl;dr: Your personal evolution, invested and extended into your creations, makes the stakes for failure higher than anything else you could possibly do. If your art fails, that means you fail as a person. Nothing will motivate you to succeed more than that.