I think it's all been said already. :) Focus is the main problem here. I have the same lens, and I can see the same close range softness. I have the macro version, and it's really not a good macro lens. You shot this at f/10, which is too slow for your light. In such low light, you should be shooting close to f/2.8 to get your best shutter speed. Also, try to avoid major cropping of an image. This lens has a cloudy softness to it that really shows up when you crop the image, and I can see that here. But there's certainly promise in an image like this. Keep working on the technicals, and keep following this little guy around. :)
Not much to add to Judi's comment except that I was shocked to see this so near the bottom until I looked at the full size picture. The shallow DOF is cool but the nose/eyes would have needed to be crystal sharp to make the shallow DOF look purposeful. It also feels tilted a little to the left even though I'm sure it isn't. Just an effect caused by the little guys body running along that side.
I'd left a post comment, but forgot to post it. I could see that there was a shallow dof from examining the leaves. I thought it was a smashing composition, but wondered if lizzie hadn't moved: it could be that, or it could be the low iso, or the small dpc, but the head doesn't stand out as being in focus.
Just to add to my comment...the focus may have been aimed at the head....but look at your shutter speed...it is way to slow for a handheld shot of this calibre. A rule of thumb is if your lens length for the shot is at 70mm, then do not go below 1/70....again...if you were shooting at 200mm, then don't go below 1/200. Mind you some people do have steady hands and can manager slower speeds...but you can see the movement of the camera affecting the focus on this image.
the photo is pretty out of focus, maybe because of the movment of the lizard. faster shutter speed and small aperture will fix this. i do like the colors and how they compliment each other though, so keep trying