Talents:

Single target:

Single Target Talents

Mythic+ / Cleave:
Note: Premeditation and WM are interchangeable, this means both are valid options.

M+ Talents

AoE (5+ targets/alternative M+ build):

AoE Talents

Gameplay Loop and Opener:

The gameplay revolves around stacking damage amplifiers. The main cooldown is Shadow Dance. It allows you to replace the weak builder Backstab with Shadow Strike. In practice this means you will try to use Symbols of Death on cooldown and align Shadow Dance to it.
Combo point generators follow the following order:

Shadowstrike during Shadow Dance, Stealth or Vanish.
Backstab if you are outside of Shadow Dance.
Use Shuriken Storm instead of Backstab if you have 2 or more targets.
Use Shuriken Storm instead of Shadowstrike if you have 3 or more targets. (4 if the Premeditation buff up, if you have the tier set or if you use the Akaaris Soul Fragment Legendary Power in combination with higher Deeper Dagger ranks)
Note: Use Shadowstrike to apply Find Weakness to additional targets in 2 or 3 target cleave situations.

Use a finishing move if you hit 5(4 if talented in VigorMarked for Death or on exactly 4 targets) or more Combo Points. Finishing moves are split into two categories, Maintenance and Damage. You usually want to keep your maintenance buffs/dots up 100% of the time while shifting the use of your maintenance spells outside of Symbols of Death..
This means you will use your finishing moves under the following conditions:

Use Slice and Dice if its not up or you are within pandemic.
Use Rupture if Slice and Dice is up, if there is no Rupture on the target, Rupture can be refreshed and if the target survives at least 15 seconds.
Use Rupture if Symbols of Death comes off cooldown soon and the remaining duration is too low to cover the entire cooldown duration.
Use Eviscerate if Slice and Dice and Rupture are up.
Use Secret Technique instead of Eviscerate if you are talented into it, you have more than one target and it’s not on cooldown.
Use Black Powder instead of Eviscerate if you have 3 or more targets and if Secret Technique is on cooldown.
Note: if you have 4 or more targets, stop using or refreshing Rupture. Note: if you have 6 or more targets, stop using or refreshing Slice and Dice.

Cooldown Usage:
Use Symbols of Death On Cooldown
Use Shadow Dance during Symbols of Death with low Combo Points or if you are about to cap on charges.
Use Vanish on cooldown outside of Shadow Dance.
Use Shadow Blades on cooldown.
Line up Shuriken Tornado to Symbols of Death and Shadow Dance if possible.
Have Instant Poison applied at all times.

Opener:
With Premeditation:
Shadow Strike -> Rupture -> Shadow Blades + Symbols of DeathSchadow Dance -> Shadow Strike -> …

Without Premeditation:
Shadow Strike -> Slice and Dice -> Shadow Blades + Symbols of Death + Shadow Dance -> Shadow Strike -> Shadow Strike -> Rupture -> …

Gearing:

Covenants:
Kyrian is the strongest choice for single target heavy encounters.
Venthyr is the strongest choice for encounters with adds, multiple targets or Mythic+.

Bone SpikeApply Bone Spike to every target as soon as possible if the target survives for at least 20 seconds. Use Bone Spike else if you are about to cap on charges. Use Bone Spike right after applying Slice and Dice (after the initial Shadow Strike with Premeditation) in the opener sequence.
SepsisUse Sepsis on cooldown. Right after Slice and Dice in the opener.
FlagellationLine up Flagellation to Symbols of Death.
Use Symbols of Death right after Flagellation if you don’t need to hold Symbols of Death for more than 10 secs.
Echoing ReprimandUse Echoing Reprimand on cooldown but not during Shadow Dance.

Covenant Conduits:
The Covenant Conduits don’t seem to compete with the stronger Potency Conduits.

Night Fae – Sepsis ShockThe impact of this is rather low.
Necrolord – Sudden FracturesThe conduit in essence adds another chance to critical hit.
Venthyr – Lashing ScarsIs with current tuning the strongest potency conduit.
Kyrian – ReverberationWhile behind in single target it could be a strong pick for m+.

Potency Conduits:
The majority of our Potency Conduits are passive. The only one with a potential rotational impact is Perforated Veins.

The priority is:
Lashing Scars > Perforated Veins > Deeper DaggerStiletto >= Planed Execution

Deeper DaggerEviscerate benefit from it always because the buff triggers before the Find Weakness shadow damage part. The Conduit currently increases all shadow damage, this can make the trait competitive if you have a lot of shadow damage sources or use the Finality Legendary Power.
Perforated VeinsIs currently one of the strongest choices and only becomes stronger with the tier set or double legendary. The gameplay change this trait implements is to use Backstab between casts of Shadow Dance  to consume charges. Only when you unlock the second Legendary you will use Backstab during Shadow Dance when Shadow Blades is up and you are on high stacks.
Planed ExecutionLoses Value on more targets but is a very strong single target choice.
StilettoIs a strong choice but loses value if you delay your Shadow Blades casts.

Soulbinds:

Legendary Items:
The best choice for single legendary is the covenant one on Venthyr and Kyrian. Night Fae and Necrolord use Akaaris as single legendary. The choice does change from Akaaris to Finality in mythic plus.

You will always use Akaaris on single target and Finality else as your primary legendary once double legendary unlocks.

Akaaris Soul FragmentThe best single target legendary. Becomes more dominant with 9.2 because it procs Perforated Veins.
Mark of the Master AssassinGains a lot of value in Mythic+ because you can use Stealth between pulls to get a higher uptime. You want to use Vanish during Symbols of Death when using this Legendary Power. Don’t use Vanish if the Mark of the Master Assassin buff is up. Is probably less desirable with 2 sec uptime.
FinalityBecomes the better choice in Cleave situations and is very strong in AoE.
The RottenIs competitive with Finality on single target but does not work well in Cleave or AoE
Deathly ShadowsCompete with Mark of the Master Assassin . You want to use Vanish during Symbols of Death when using this Legendary Power.
Essence of BloodfangIs currently not tuned high enough to compete
Invigorating ShadowdustIs a interesting alternative to Mark of the Master Assassin in combination with the Night Fae Covenant
Resounding Clarity(Kyrian)Is the strongest single target Legendary Power if you play Kyrian.
Obedience(Venthyr)Is the strongest single target Legendary Power if you play Venthyr.
Deathspike(Necrolord)Is after the nerfs to week to consider.
Toxic Onslaught(Night Fae)The buffs to this legendary in 9.1.5 makes it the strongest legendary choice if you play the Night Fae Covenant.

Secondary Stat Prioritization:
Versatility >= Critical Strike > Mastery >= Haste

Secondary Stat Plot (no Legendary Power, no Soulbinds, no Covenants):
Single target:

Dungeon:

Macros:

Shadow Dance + Shadowstrike: Use this macro if you use one key bind for Shadow Strike and Backstab.
#showtooltip Shadow Dance
/cast [stance:0] Shadow Dance
/cast Shadowstrike

Shadow Strike/Backstab:
#showtooltip Shadowstrike
/cast [bonusbar:1] Shadowstrike; Backstab; Gloomblade

Secret Technique/Tornado:
#showtooltip
/cast [talent:7/2] Secret Technique
/cast [talent:7/3] Shuriken Tornado

Sap/Kidney:
#showtooltip Sap
/cast Pick Pocket
/cast [combat] Kidney Shot
/cast Sap

Weakauras:
Shuriken Tornado: link
Shadow Techniques: link

FAQ:
Can i pick Premeditation instead of Weaponmaster on Single Target?
Weaponmaster is usually the better choice so its advised to use it.

How does Pandemic work?
A new applied spell can take up to 30% of an existing spell and extends the new applied spell with this duration. Keep in mind that those 30% are calculated from the new spell you cast.

How does Shadow Technique work?
Shadow Technique procs on auto attacks, every 3rd auto attack has a 50% chance to proc it and your 4th has a 100% chance if it didn’t proc on the 3rd. Missed attacks do not count towards this.

About:
I am Fuu(fuu#7750), Rogue Theorycrafter since Legion. If you got additional questions, found mistakes or want to have something covered in the guide send me a DM on discord. You can do this by clicking on this link. I also maintain the Wowhead Guide for Subtlety Rogue that you can check out if you want a more in detail option.