As a simple rule of thumb, to get crisp, sharp photos without any camera shake you should be using a minimum shutter speed of 1/60 sec for wide lenses and when using anything else follow this simple rule...
Focal length = minimum shutter speed....so...
75mm you should use a minimum shutter speed of 1/75sec
100mm you should use a minimum shutter speed of 1/100 sec
150mm you should use a minimum shutter speed of 1/150 sec
300mm you should use a minimum shutter speed of 1/300 sec
....etc
If you follow that simple rule
generally you will eliminate most of human introduced camera shake. If your chosen settings will not allow fast enough shutter speeds you'll either have to increase the iso, choose a smaller F stop, use flash or additional lighting or finally use a tripod.
Be aware that a tripod will only help remove movement of the camera and will not prevent blurred pictures if the subjects are moving.
Hope that helps a little.
