Focus on your subject with the AZ421. Press half-way down on the shutter button to focus on your subject, when you see a green box around your subject in the AZ421 LCD, that is your indication to take the photo.
Simply press the shutter button all the way down now and take your picture.
You can also use the Image Stabilization mode on the AZ421, which will allow the camera to automatically compensate for unsteady uses or accidental shakiness.