When we press the shutter button there is some movement of the camera which causes the image to be blurred. At faster shutter speeds there is no noticeable effect on the image but at slower speeds the blur becomes noticeable.
To eliminate the blur we can do the following things:-
1) Faster Shutterspeed: By opening the aperture wider or by introducing more light, we can increase the shutter speed and eliminate the blur. If you are using a 50mm lens the shutterspeed should be atleast 1/50th of a second and if you are using a 250mm lens it should be atleast 1/250th of a second. This is because the shake is magnified as the field of view gets narrower.
2) Steady tripod: Putting the camera on a tripod is the best way of keeping it still, using a remote is better as you don't have to touch the camera.