I'm fairly new to macro photography, and heck to photography in general, but there was one thing that helped me tremendously.
I covered the viewfinder and went with live view. With live view, you can zoom in to see just how good the focus is on a close up item. I have my camera set up to show how changes in camera settings look in live view. So it's truly live view.
I also have an LCD loupe which really allows a great look at how the picture is looking. With the loupe and live view, I can really focus down very finely. I think I prefer manual focus with my macro lens, but really need to use it more to find out what works best for me.
Anyway, that's my small addition to the thread. Really, those are great photos that you posted above. As a plant person, I really like the dandelion photo as well!