Mapping is one of the main things when making textures for toribash,
you should start there for that case, as your mapping for this head looks
... Not that great. But as for drawing in general, like Ben said, just draw
more and more. Get used to your table, trace things to learn how to control
it, try placing it in different positions to find what's more comfortable for you,
and overall, just use it more and draw more.