some subjects for art practicing?

you need to practise different kind of textures, lights and shadows.
Start with still life, a simple cup of tea with a single light source. Study it, look how the light behaves when it encounters the cup's surface and the material the cup is made of. You need to know what you are drawing and you have to think tridimensionally, just life if you were sculpting., then you can move on what you like, portraits, landscapes ecc..

do it until you get right