I have run a lot of CoS10-15 and here are a few tip for people interested in small optimizations beyond "have a comp that can use the buffs". Hopefully some people find them useful!
1) If you are on someone else's passenger mount and the mount-owner is pulled into the boat at the beginning of the instance then you will be dropped in the water and you can mount up on a water strider to reach the beginning of the instance slightly faster.
2) Scouts deal a nasty dot on the first person to aggro them, no matter how fast they are taunted after. So be ready for that or let the tank aggro them.
3) If you are unable to stun a scout you can interrupt the "sound the alarm" cast. The scout will not recast it and will simply melee the tank until killed.
4) The engineering (Goblin/Gnomes also) orb that disables all robots is now able to spawn in M+! Check for it, the robots suck.
5) The adds that the first boss summons if you do not deactivate the last three pillars are easy to handle (usually) so you can save time by pulling the boss sooner.
5b) The summoned adds do not drop sanguine puddles or cause bolstering. They do cause additional volcanoes and necrotic stacks (!) though.
6) You can skip the robot after the first boss by simply running past it, it will not chase you into the second boss area. I usually kill it though.
7) If the broken trap is repaired (hunter or blacksmith) while a miniboss is stood on it then it will kill that miniboss without being consumed. This means it can be used to quick kill two minibosses.
8) THEORY: Since 7.1.5 it seems that you will always get at least one offensive (haste/crit/dmg) and one defensive (hp/damage reduction) buff available.
9) If you wipe on the last boss, buff items that cannot be triggered by your party will become usable.
eg. The crit orb is up and you have no DH or lock, then after wiping on the last boss any group member can pick it up on the run back.
NB: If you have a lock/DH and he's just been lazy, other people cannot use the orb even after a wipe.
10) There is a stealthed Dust Lily Agent that stands on the last boss' balcony after you kill him and will teleport you out of the instance.
EDIT, more tips:
The enforcers (that call minibosses before 2nd boss) do not move while casting detonation so the tank can also LoS it.
An enforcer can spawn in any of the four "corners", when killed another will spawn after a fixed time in one of the other three corners. Be careful about pulling enforcers out of their spawn-corner as this enables a new enforcer to spawn on top of you.
You can avoid the charge the last boss does by being at max range and running, using a speed increase if not at max range, or blinking out of the way. This reduces damage taken on that fight a LOT.