I have this lens on a 450d
I started off using Aperature mode and going for the smallest aperature I could get away with whilst keeping the shutter speed quick enough.
worked great ... but still had a very small DOF so insects had there heads in focus but everything else blured.
flowers more more sucessful as I could use a tripod and shrink the aperature to f-16
I only lasted 2 weeks though before I gave in and bought a flash ..... Manual mode, F/22 and 1/200 exposure and insects are now fair game