One of the most common mistakes I see is failure to hold the camera correctly, which leads to blurry photos.
Most people hold it like the image on the left. The problem is that the thumb is trying to support most of the weight of the camera, and that's very unstable, especially with a long lens.
Instead, make a shelf with your palm and rest the camera on it. You can still reach around and turn the zoom dial, but the camera will be much more stable and you will get a sharper photo.
Also, remember not to lean forward and throw your balance off. Stand erect to take the shot and it will be more stable. If you need to get lower, kneel down.