try to make your cuts smoother...
zoom in to 400-500%...use pen tool (its the best)
and try to keep clicking on the edges of the body, make sure you don't get any background included....if you make a mistake delete that last click and try again...
and when you are cutting the hair, zoom in a bit more, and cut slowly and keep it as smooth as possible....then later when you paste your render on a transperant background, defringe your render to remove any slight borders remaining, and then smudge the hair very little to make it look better (dont use any hair brush to smudge, use soft round brush, and remember to only smudge it a bit).....And remember never feather your renders dude....thats not the renderers job, thats the designer's job...just keep your renders smooth and neat...
and dude, i think you have a very high mouse speed, i think you should go to control panel and lower your cursor speed, when rendering, and then later change it again...
hope this advice helps, keep improving...