I know, its difficult. I had the same problem. Too eager to press the button and as a result getting the moment to early. It took some trial and error and a lot of discipline to press that button a fraction of a second later!
With my digital camera you can either tell it to focus and take the picture at the same time so there's a slight delay, or focus before you take the image so it's ready to go. I was used to the first method, so now I always expect a delay