Using a telephoto lens to get in close to the action or sneak up on a subject from a discreet distance is terrifically exciting, and can yield great pictures. But the high magnification of long tele and zoom lenses accentuates the effects of camera shake caused by your inability to hold the camera and lens absolutely still. The effects of wind, moving or shaking floors, residual vibration from camera mirrors flipping up just prior to exposure, atmospheric haze, and heat waves can also add problems.
Cold, tired, been drinking stimulants (coffee, tea, or cola)? They add to your problems. Avoid them all if you can and don’t despair.
When handholding your camera and lens, start with a fast film, ISO 400 or higher. This will allow you to use higher shutter speeds (1/1000 sec and above) and minimize the effects of shake in a variety of lighting conditions. Use the proper stance: arms closely tucked into the body, elbows partially supported by the chest or abdomen, lens and camera balanced by the left hand and arm.
Practice supporting and focusing the camera with your left hand, aim the camera slightly above the subject, take a deep breath, let the view drop...