My damage as Sub seems really low when compare to other class Currently ilvl 389 and I think I need some help with rotation.
For AoE:
Do I use Shuriken Storm then at 7CB Rupture and then use Black Powder and only use Rupture to refresh? Then use Secret Technique during Shadow Dance and Cold Blood?
Do I also have to keep Slice and Dice up as well?
I also use my CD as possible.
I feel like I am doing a lot dps when I compare to my other melee class with almost the same ilvl.
According to some people here, sub is the braindead easiest spec to play. Maybe those experts can shed some light.
Why are you doing low damage if all you gotta do is shuriken storm → blackpowder spam 
For any AoE pull, your first goal is to get rupture on every target as quickly as you can. Don’t spend too much time thinking about it. Just try to get it on a majority of the pull. After that you can start your sec tech/dance rotation.
Priority:
Basically, you want to get the Shadow Dance/Secret Technique rotation down to muscle memory. Your goal is to get your Dance Macabre stacks to 4 and then pressing secret technique.
After this, just keep doing your filler rotation (which depends on how many targets are still up) and then you can worry about refreshing your Ruptures, CCing, anything else.
That is your AoE rotation and will yield you get the best burst. Practice on the cleave dummies.
Source: I am a KSH Rogue 
This isn’t the correct AOE set-up when Tornado is up. Tornado set-up is:
Tornado/Symbols/Dance-> Rupture-> Eviscerate-> Black Powder → CB+Sectec. Tornado gives you all the CP you need to execute all these finishers back to back so absolutely no builders are needed and with time you have on the back end you shuriken into black (similar to the SS/Evis finish of a ST rotation). And you want to make sure you Thistle before all this as Mastery scales insanely with AOE. Maybe it’s a little tweaked in Mythics but you won’t put out chump numbers doing it this way in M+.
See above for AOE. Downtime AOE should be distributing Rupture around between Dances IF the stuff will live 15~ seconds.
For ST it’s pretty similar sans Storm. you need to talent out of “AOE spec.” You do need to keep S&D up always but premeditation can help keep it up so our maintenance isn’t all that bad (but not as good as Assn).
Your ST will be
Symbols->Dance-> Gloomblade → Evis → SS → CB+SecTec-> Vanish → SS
Always pair Symbols with Dance. Always pair CB with SecTec (macro it) and on Multi always thistle with dance. I try to lean towards keeping Thistle aligned with Dance in ST as well, but you should definitely use it when energy starved. Never Rupture in ST Dance
Clean play gives you real strong benefits once you’ve got your ST/AOE dance rotations down. Knowing when to Cloak can offer a lot of safe slap time that other classes don’t get (Raz knockback for example), using step to make sure you can stay on stuff/aren’t sprinting to stuff in heavy movement. Definitely macro CB into SecTec not getting immediate clicks here can cost you the vanish+ss follow up. Also optimizing CP – 6 or more outside dance for damage finishers and 5+ for in dance (it’s pretty easy to be in the 6~ range with these rotations though). Then, of course, learning fights. Whiffing a Dance HURTS.
Also one more thing while you may want to throw in as many additional clicks (shuri in ST on top of the general rotation) to get more danse stacks Not worth it. The way CB+SecTec works is you hit with SecTec and then the follow up hits occur. If your dance ends before those follow up hits you will lose the danse buffs onto the damage.
Some typical WAs I have to keep efficient are S&D tracker. Rupture on target tracker and a Finality - Rupture tracker (not needed, like Evis and others just play naturally but after a dance always update your Rupture with a Finality Rupture).
I recommend joining the Ravenholdt discord and checking out the sub faq. all this info with more detail, sims, bis, etc.
Overall, Sub SOUNDS daunting but once you get your Dances down it’s quite easy. There’s just so many nuances that aren’t super clear even just reading Talents. This is one of those specs that just has to be mathed out to an efficient execute and theres no real wiggle room for deviation.
Good stuff!
Yo heads up, ravenholdt discord is actually your best source.
Everyone here is giving you complicated explaination to do in aoe pulls.
It’s not complicated in the slightest.
Guarentee you will do phat damage if you follow my casual af rotation.
At the start of aoe pull you:
DO NOT BOTHER RUPTURING ON TARGETS HIGHER THAN 4.
The reason why I say this is because things die FAST in this game. If youre in higher keys where mobs die slower, I STILL do not recommend rupturing anything past 4 targets.
The time it takes you to rupture them for extra dps down the line is negligible for the amount of burst you will be doing with those GCDs.
In those precious seconds you take to rupture everything, the mobs are ALREADY at half hp. You lost out on actually doing the damage required to kill your targets and simply put out less dps.
Ive tried multiple times, and maybe I just am not fast enough, but when it comes to AOE pulls, I have ALWAYS been top in meters in all of my key groups 10-15.
Though, what others may recommend at higher keys may make sense just because mobs tend to last a little longer.
At the end of the day, your cds are up FAST. It is actually the ONLY way you deal significant dmg and should always be spamming them in conjunction (except shadow blades but even that can be spammed if you make sure it will be up by the boss.)
Sub is probably the easiest for aoe rotation as it really just comes down to popping shadow dance + symbols then spamming your storm and black powder.
you advice him to look at ravenholdt discord guide but gave him your own wrong aoe opener.