*Single point focus--get it exactly on what YOU want to be the sharpest point.
*Smaller aperture--f/5.6 doesn't give you enough depth of field at that focal length.
*increase your ISO to 400 or 800, to give you faster shutter speeds, even at the smaller aperture. I get good images at ISO 800 on my D3100.
If you want to do shots like this, you really need a 300 mm lens absolute minimum. I started out with the 55-200mm like you, and my first upgrade was to the 55-300. My next upgrade will be to the Sigma 150-500.
working on it in Middle TN Nikon D3100
35 mm 1.8 Nikkor 18-55 mm Nikkor VR 55-200 mm Nikkor VR 55-300 mm Nikkor VR 150-500 mm Sigma OS Feisol CT3471 & Markins M20 ballhead