You need to whack more joysticks around to get that smooth hand precision surgeons have.
If you ask me, learning to draw consists of two big challenges: Study and practise. Why "Study"? You gotta look at things and actively think of how you perceive them, how the lighting works, what makes the thing this specific thing. For instance, when looking at my avatar, you may think it's as easy as hat and monocle, but closer inspection reveals spiky sideburns of sorts and wavey hair, those being integral to the portrait. Only if you notice and analyse such properties, will you be able to replicate things the way you see them.
Also, if you think drawing with a mouse is too jaggy, try to use "correction", a lot of free drawing programmes have it.
Lastly, feel free to think outside of the box. There's a lot of ways to generate imagery using computer programmes, just like there's plenty of tools for drawing on paper/canvas and numerous techniques to use those.
(e.g. making mosaic tiles using polygon selection and fill bucket)
