Cynthia is correct, I do it without thinking, it's all part of composition.
If I had thought about it, I would have passed that tip along myself. Trouble with being a professional photographer for many years, you tend to do a lot of things instinctively after a while and forget the little steps you do without thinking to get the end result.
I actually used the technique Cynthia mentioned of pushing the shutter button down half way to compose the image in freeze frame to get the new leaf on my Epi in the thread "New Growth Everywhere".
Some cameras like my Olympus need horizontal or verticle lines to focus on, so I pick the edge of a leaf, push the button half way, move the camera to compose the image and then gently push the button all the way to take the picture.
All this in a second or two.
I would suggest people look around for a cheap, light tripod to put your digital cameras on so that under low light you don't get camera shake, and also it helps when you are setting up your plants to get a good shot, as you have the camera in the same position all the time. Then it is easy to zoom in or out, or move the plant one way or another to show it at its best.