randomness like Glorifico's picture

Well, you should always try to be original, the medieval, cartoon, and simple themes have been over-done, along with modern and sci-fi. If you're new-ish to texturing, why not experiment and just make completely random textures of random things, or take a block in minecraft and retexture it into some other material you think should be in minecraft that isn't. You've got a lot of freedom, make minecraft your own! And when you've made enough textures that you feel are fit for public consumption, upload them! Maybe someone else will like what you've done!