Just got the Sigma 100-300/4 for the D700 in a killer deal. Probably my last lens acquisition for a while given the current shaky state of my job, and man, what a beaut. Will be posting some images from it soon.
Other than that, what lens are you using or is it a point & shoot?
Better compositions, better lens, heavier PP in that order.
EDIT: Ok, it's a superzoom with max aperture of f2.7. Leave the silly auto, macro and landscape modes at the door and go aperture priority for a while and start experimenting with shallower depth of fields for subject isolation. Aperture priority locks your aperture to your choosing (usually wise to set it at max aperture=smallest number) and the camera does it's best to expose correctly by adjusting shutter speed and ISO (if you have ISO auto controls). Aperture priority might drop your shutter speed too slow and give you motion blur but without knowing what/when/how you shoot, it's up to you to learn how your camera exposes and what's the slowest shutter speed you are comfortable shooting depending on the scene.