Echoing what Brent has said above.
The section of the photo that is in focus can be very thin in macro, adjusting the F Stop will help - to a degree.
I have the Kenko tubes and they do work well, but it does take a lot of practice.
Using live view is one way to see exactly what you are doing.
The other trick I use is to take a series of shots moving in and out (by maybe an inch or two, taking a shot every 1/8th of an inch. So I am focusing by moving the camera rather than turning the focus ring. I don't have a focus rail but probably will get one, moving in an out manually can be tricky.
Forget autofocus. I now only manual focus in close up macro shots.
Have you tried different ring combinations, one ring, two different ones in various combinations and all three? Makes a huge difference.
Have you tried other lenses?
As was suggesed, post samples and explain your settings. Macro can be a lot of fun once you get the hang of it.
Oh - and don't worry about a low 'keeper rate" I probably keep one in 20 (or 30 or 40) shots. Shoot lots and lots of shots.