Watch the C m11 Tuning online guitar lesson by Vicki Genfan from Essentials: Open Tunings
Make sure you're changing from the Cm11 to the Gm11 on the up beat of 2! This bass movement really gives the peice its bluesy lilt. Feel free to add any embellishments that you can find while you're playing these simple barre chords - especially the iv and v chords (Am, Gm). When playing the B section it can be tricky to keep your bass note down on the AbM13 chord while you're taking all the other fingers off! Again, slow it down and isolate it until you really get this movement ingrained in your muscle memory!