Well, there are all types of girls with all sorts of features, but if you're going for a straightforward feminine look, here are some things you can do to "femme up" a character:
Thin the eyebrows.
Thicken the eyelashes.
Make the chin pointier, jaw less square.
Make the cheekbones higher and the cheeks fuller.
Make the nose smaller.
In general, the head should look a little smaller than that of the male.
Make the lips fuller.
I took the liberty of playing around with one of the male characters from your comic, so you can see what I'm talking about:

As for bodies, it's all about the curviness (particularly around the hips) and proportion. Other than that, just remember to make sure everything abides by the laws of gravity.
This is just a starting point...like I said, there are all types of girls, and they're all fun to draw. Be sure to take a look at
Wapsi Square and the
Pants Press sketchblog to see some examples of nicely drawn females.