Any time you are shooting something this small, depth of field and motion are your main enemies. To get even a half way decent dept of field, you want to be shooting at f22 or even f32 if the lens doesn't fall off significantly at higher f-stops. Using a tripod is a must, but locking the mirror up and/or a cable release will also help. Finally, the thing that I have found that helps the most is using a really short flash duration. I usually use twin strobes, but shooting at f32, the duration of the flash is pretty long. I get the flash heads as close to the subject as possible, go to manual, and try to get the exposure correct using 1/16th or 1/32 power. That gives you a duration of less than 1/10,000 and really reduces blur.
Roy