Do you use a mouse or a tablet? It doesn't look blurry to me, I just think you should try varying line widths and putting the pen width on pressure setting on the tablet to get the smoother pointed look to the lines.
Also, the main thing that makes that other picture look good is just that the pose it more fluid and natural looking and that will just come with practice.
If you are drawing on a low resolution canvas and zoom in you will see the anti-alias that Sai puts around its lines. Work larger (at least 300 DPI in dimensions equivalent to physical media) and it'll be fine.