So there is such thing as an art scale? 1 to 10? Or how does one become the best?
Depends on perspective. At least thats what art people tell me.
There is a 1-10 scale if you're being graded in class. Not when you're doing art for a living.
For beginners and amateurs, you have to make sure the painting represents the object correctly. That means it shows a good understanding of perspective, shadow, proportions, colors work together and don't clash, etc.
Then there's different styles of paintings, abstract being one. At that point it's more about what the art represents and the story behind it but there are still rules. And it has to be pleasing to the eye, you can't just throw a bunch of random colors together.