Using preset shapes to make nice smooth lines and shapes
Once you have cleaned up your graphic like this cute bumblebee and you have all those rounded edges you want to make smooth.. Try using your shapes tool...
It is a great way to make them smooth everytime..
First I added new layer then After I have close to the shape I wanted I
took it and moved it ontop of the wing. 
When I did this then I just worked
on it moving the edges until they made a great fit over it like this once
you have it like you want it..
go to your layers and promote it to a Raster layer.. you will notice there is a little bit on the inside of the line that
you will need to touch up... to do this you can get the color with your
eyedroper and use your paint brush to fill it in... You can also use your clone tool... 
Once you have this go to your draw layer and remove any of the outline that is on the image you don't want to have show.. to do the opposite wing I duplicated the layer of the shape of the wing.. mirrored it and then fit it around the other wing.. Then finished it up like the first wing.. Here is my bee ...
Now doesn't he look dapper...LOL ! Have fun!
By Barbara