Calcs are good to give you a general idea of where you want to go with your skills but start playing, figure out what your comfortable with and use consitantly and go from there. In my case for large groups/strong/elite I start with WW, single the lows/adds then stun/dot/bomb while bub/healin Khem. The only probs I've run into have been adds popping on me from someone clearing the way earlier or not paying attention to what I'm doing.
Jax