When I say "other subjects" I mean can you paint things other than general character artwork? It has kind of a "pin up" look even though its not the usual subject matter at all.
Its a character in front of a pretty basic background.
If you want to make money you'll have to learn actual illustration.
See, pin ups just aren't ever an interesting composition and they almost never tell a story. What you've got there is just a piece of a story, but your style is really appealing.
I say "keep it up with other subjects" because I see way too many artists as one trick ponies, and its almost always doing characters.
Make sure you know how to paint landscapes, objects, interiors, etc.
Don't get me wrong though, I think you should still keep it within your niche. When I say it reminds me of "ICO" I say that because of the stone elements, the armor, and most importantly the natural background. It has a very fantasy feel with the materials being overall made out of nature.
So, "other subjects" really doesn't have to include things like cyber kinetic futurism from the year 3000 or something, keep it within what you are genuinely interested in.
I don't think many people on here are good enough for promo work, but when good enough actually just means experienced enough. You'll have to work your way up somehow to build a name for yourself.
You can start out by doing concept art for indie games or making illustrations for trading card games.
Do you have a blog? I'm curious about if your other work is within that niche.