Textures, textures, textures!
They make a drawing look more interesting. Gives it more character and flavour. Just changing the texture can give a whole different look to a drawing. That makes me feel happy. I find that I don't have to buy expensive tools to make interesting texture. Some tools can be made with stuff I find around the house, and some can be purchased at a provision shop for a couple dollars. Here are a few things I use. And here is a Youtube video I did about it: https://youtu.be/jjGVwYkHVRc