Photographer's general rule of thumb to avoid camera shake which can cause unsharp pictures:
If your zoom lens is set at 100mm, make sure your shutter speed is 1/125 or faster. If 200mm, then set to 1/250 or faster etc. If anything slower than than that then I hope your lens has image stablisation or your camera is on a tripod. To achieve fast enough shutter speed you may have to open up your aperture or increase your ISO. Also you may want to cut down on the caffeine.