The artistic filters in Photoshop usually looks flat due to the lack of textures. Artistic filters can look more realistic by adding a texture to it. Learn how to add texture to your artistic filters so it looks like a real painting.
If this painting is not going to be printed on a canvas, try adding a "Pattern Overlay" layer style and select an artistic canvas as the pattern with the blending mode as hard light to make the painting look like it was painted on a canvas.

10 Random Photoshop Photo Editing :
10 Random TutorialKit Materials:







More Photoshop: