They can be tricky indeed. I've tried it last weekend(posted/will post in post your best flower shots and 100Lmacro thread) and while mine are far from perfect I've got a few tips:
Try to isolate 1 or 2 flowers( this means often on your belly in strange postures).
Try to use a small f-number(again for isolation).
Keep an eye on your exposure, I used spot-metering on the flower and raised the highligts in LR and lowered the shadows to darken the background. PP can make quite a difference on the finished picture.(if you want to I can post some before/after pics)
Best is a soft sunlight but I also used my macro flash for some shots.
And practice, practice, practice while they are still flowering.