Colour scheming and things you can fix up and find out what suites best over time, just have play with it from time to time.
Btw if your into Flash (Iv'e been making a platform game for learning flash and actionscript, I have programming experience and game programming so it's not too hard, but anyway), you can create some very smooth hand drawn shapes quite easily.
As it's vector based for drawing, you could use the brush tool to free-hand draw your butterfly and any other shapes with a high smoothing level and then just drag any edges that are too thin/thick in or out. So basically you can get some pretty smooth graphics
I use photoshop myself, but am unsure of any methods of achieving the same result as I explained you could do in flash.




