Well, Personally I start each macro shoot above 1:1 (almost always shoot above life size now) in M mode, with the settings ISO 200, 1/160 shutter speed, F/13 with the reversed 50mm @ F/2.8 and the AF 360FGZ @ 1/32 power. From there i mess with it a bit until im happy. i suggest you play around with ur setup and find that group of settings that work best together. Doing this simple thing has helped tremendously with getting *the shot*
Oh and I suggest always shooting in M mode when shooting macro's.