A set (usually 3) of AUTO extension tubes is what you need. This will allow the auto diaphragm mechanism to operate normally. I would use your lens @70mm rather than at the wide end. This will give more distance between lens and subject. DOF is very limited and normal focusing is not the best way. Instead, decide on your approximate subject area by experimentation, set the focus to infinity and move the camera towards the subject until the image is sharp. I wouldn't advise using the lens shorter than 50mm for macro work but between 50 and 70 you should get some good results. Using tubes will result in reduced exposure and this will depend on the amount of extension and degree of magnification but TTL metering will automatically take care of this. Get some tubes, shoot some pictures and you will discover a whole new set of problems to solve like camera shake, tripods, flash etc. but feel free to come and ask.
P.S. Try the Macro Forum .