What do you mean proccing Arcane Shot?
Your basic MM rotation should be: HM > SrS > CS > RF > Readiness > CS > SSX2 > ArSX2 > CS if it's up, if not, SSx2. The rotation takes a bit to get used to, but always remember to do SS in 2 shot bursts. Use CS everytime it's up and burn off extra focus with ArS. If AimS procs, fire it when you can. Even in basic Tier 10 you should push 6-7k easy with this rotation.