There used to be some formula photographers used to pass around to each other and I've forgotten it.

Something like - when using long length lenses, keep your shutter speed at least twice the focal length. Meaning, if you're at 100mm, keep your shutter speed no less than 200th or 250th a second, get it?

And if you're tired... Good luck... And get a monopod...

-Lew ;-)