Do you have any references? What type of art will you sell?
Either way, I think opening a shop and allowing people to pay as much as they like is a good starting point as you get a real idea of what people want to pay, then you can set your prices of that.
5 tbt. i'd critique this, but honestly there would be too much to say. at this point, just practice a lot. even if you think it looks bad, dont stop and keep going- at least finish it half assed if you have to. trust me, you will improve. at the same time, look at other artists with a similar style as you and study what they do that you like, and compare it to your art to see what youre missing or how you'd like to change it to make it better. this is optional, but it does wonders. i learned that just by doing freebies for people, i drastically improved over a short period of time because since i drew so much, i learned from more mistakes and managed to experiment a bit to discover new and better ways of drawing for myself