I don’t know if this is a technique, but when I was painting my art work, I tried to show the bumpy texture. To make it bumpy, I dipped the brush into the paint and got a lot of paint on my brush. Then, I  started from painting small proportion (If I colored it in big places, I would get smooth texture). Sometimes, when I did not like the color, I colored other color on the top to cover the color that I didn’t like. That gave my artwork to have more bumpy textures.