this may sound cheap but i did it and it helped loads
basicaly have a sketch the sixe of the drawing area (can b ur own or a print out)
config tablet so that for that app the drawing area on the board represents the drawing space on the comp(canvas)
and trace it
i donno y but i prefer to draw in corel rather that photoshop
its cheating i know but u will learn better conrol of ur hand eye coord wen using it then draw a similar style with out tracing
it worked for me check on my site under projects and wacom
this was the second thing i drew after my tracing session an im getting better evry time and so will u its just pratice