Like Swikan, I haven't been doing this thing for too long. So, for better perspective, here's a chart of the evolution of my main character's design from about a week after I first started teaching myself to cartoon to about a month ago. The last image is the only one from an actual comic, and is also the only one done on my Wacom.
The biggest change would have to be making Andrew's cheek bones more defined, as well as making his head shape a tad feminine. I still haven't naied his hair yet.
For a long while, I made my character's heads about 1 1/2 the size of their trunk, but lately I've been try to shrink the heads to about 2:1 of the trunk. For my adult characters, I'm aiming for 3:1, but I haven't had much practice at them and so they've been turning out a bit malformed.