So you just got a long (telephoto) lens, but you’re not getting the quality shots you thought you would with it?  The key is to optimize everything.

First, are you using a quality tripod and head? (see the tripod section on how to use a tripod).  Keep the tripod as low as possible.  Do NOT extend the center pole unless absolutely necessary, as this makes the tripod much less stable.  Make sure you have placed the tripod on a hard, stable surface. Add weight to the tripod with a weight sack.  Shield the camera from wind.   

Second, are you shooting at a high enough shutter speed?  Open up the aperture as far as you can. Also, remember that noise from a high ISO looks a lot better than camera shake induced blur in a photo. 

Speaking of depth of field, long focal length lenses have very narrow depth of field.  This means that focusing becomes much more important.  Most people who have trouble with long lenses are simply not focusing the lens perfectly.  This is a situation where autofocus works significantly better than manual focus.

Some people put a bean bag on the top of their lens to help dampen vibrations. Or they will get a large sand bag and put their lens on top of it, which is good for situations where your subject might be moving, and re-adjusting a tripod every few seconds would be cumbersome.

 
Use a remote shutter release.  This will keep you hands from disturbing the camera.  If you don’t have a remote release, use the camera’s self-timer mode set on a fast setting.

If not using a remote release, ROLL YOUR FINGER over the shutter button when firing.  Do not stab at it, which will cause all sorts of unwanted movements.  Rest you finger, then gently roll over the button.

Finally, use your camera’s mirror-lockup mode to prevent the initial mirror slap from inducing vibrations. Most higher-end cameras have this feature