Canon MP-E65 tips and tricks needed

I just got this unique lens and would like to ask experienced owners for some tips and tricks how to use most of it. I understand basics of how to focus, but i.e. I can't see a bloody thing in a view finder when set for 1:5 magnification ratio. Best result so far (well in 1 hour of testing) is this image made with Sigma round flash. I believe sharpness can be better, so any advises are welcome.