For the “standard” build with felblade, demon blades, first blood, chaos blades, the rotation is insanely simple:
1.) Fury of the Illidari on cooldown (delay it for AoE if there will be multiple targets soon)
2.) Use “cooldowns” like potions, trinkets, racials, Metamorphosis, Nemesis, Chaos Blades
2a.) Save potions for when you have Chaos Blades up
2b.) Align Chaos Blades with Metamorphosis when possible. Usually this happens on the pull, then you use Chaos Blades again on cooldown, then align the third use with Meta. Of course certain legendaries or convergence of fates can make this timing tricky. This is really the only “complicated” part of the rotation.
3.) Death Sweep
4.) Fel Rush if at 2 charges
6.) Felblade if you won’t waste the Fury gain
7.) Blade Dance
8.) Chaos Strike
9.) Fel Rush (save one charge if AoE or movement will happen soon)
10.) Throw Glaive
(You basically never need to delay an action, just do it as soon as you can - super simple. If Fel Rush positioning is messing with you, just don’t use it on a single target - the damage gain is small enough that it’s not that big a deal.)
3.) Death Sweep
4.) Eye Beam
5.) Fel Rush
6.) Blade Dance if Eye Beam is on cooldown
7.) Fall through to your single target rotation if you can’t do any of the other actions.
Really easy rotation to execute - Havoc is more about good positioning. Some of the other talents are a bit harder, like using Momentum. The Demonic build is fun too, and pretty easy as well - you just add in Eye Beam and do a little management around extending Metamorphosis.