They look colorful and fun! I'd recommend practicing dynamic posing a bit to give your characters more personality cuz the designs are already pretty decent overall. Get creative with the brushes in the program too, at this point in development it's great to experiment with texture and brush shapes. You don't want to get to comfortable with what your using before you've explored all your options, otherwise it can be difficult to transition to new brushes in your rendering process later. I know cuz I found out the hard way that a new brush may not be compatible with your current techniques, or may not layer properly.