Macros:

Shadowstrike Macro:

Uses [Backstab] or [Shadowstrike] depending on your stance.

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

Shadowdance Macro:

[stance:0] prevents you from accidentallyactivating [Shadow Dance] twice.
/cast Shadowstrike prevents you from accidentally using [Backstab] after activating [Shadow Dance].

#showtooltip Shadow Dance
/cast [stance:0] Shadow Dance
/cast Shadowstrike

You can add this 2 conditions if you want to, [Specter of Betrayal] or any other on use trinket is usually lined up with [Shadow Dance]. [Symbols of Death] gets usually used pre [Shadow Dance]. This means this condition will never trigger but would allow you to use [Symbols of Death] together with [Shadow Dance] during the animation.
it's still recommended to use 2 macros in case you don't want [Symbols of Death] to line up or if you don't want to use [Shadowstrike].

/cast Symbols of Death
/use Specter of Betrayal

Marked for Death / Death from Above Macro:

Uses [Marked for Death] or [Death from Above] depending on what Talent is used.

#showtooltip
/cast [talent:7/2] Marked for Death; [talent:7/3] Death from Above

Same but with mouseover for [Marked for Death].

#showtooltip
/cast [@Target,talent:7/3] Death from Above; [@mouseover,exists,harm,talent:7/2][@Target,talent:7/2] Marked for Death

Vanish Macros:

My personal version of the macro, prevents you from accidentally using [Vanish] when out of combat.

#showtooltip Vanish
/cast [nocombat] Stealth
/cast [combat] Vanish

Nightblade Mouseover Macro:

Use [Nightblade] on mouseover, uses nightblade on the target if no mouseover exist.

#showtooltip
/cast [@mouseover, exists, harm][@Target] Nightblade

remove @target if you don't want the macro to only work on mouseover.

Shadowstep Mouseover Macro:

It's often quite nice to have the option to [Shadowstep] a target via mouseover during a fight.

#showtooltip
/cast [@mouseover, exists][@Target] Shadowstep

Item slot Use Macro:

Uses the Item slot, can be used for Trinkets, Rings or Engineering Enchants.

#showtooltip 6
/use 6

Item slots:
1 - Head Slot
6 - Belt Slot
11 - Ring Slot 1
12 - Ring Slot 2
13 - Trinket Slot 1
14 - Trinket Slot 2
15 - Back Slot

Tricks of the Trade Macro:

[Tricks of the Trade] on the Main tank.

#showtooltip Tricks of the Trade
/cast [target=name of tank] Tricks of the Trade

Weakauras:

Those are the Weakauras and Weakaura sets i find useful:

Shadowdance Charges for the Personal Resource Frame

Shows [Shadow Dance] charges/cooldown as a visual bar.

Fuu's Weakaura HUD

All in one Weakaura set from Fuu.

Mystlers Weakauras HUD

All in one Weakauras set from Mystler

Potato's Weakauras HUD

All in one Weakauras set from Potato

Emarline's Weakauras HUD

All in one Weakauras set from Emarline

Addons:

Addons became the highest quality of life changes that we can get. There are thousands of different addons for every thinkable purpose. Here is a list of addons that might be worth taking a look at:

Addon	Description
Rotation helper:
Aethys Rotation	Rotation helper that assists you in optimizing your gameplay
Buff Tracking:
Tellmewhen	Alternative to Weakauras that uses a bit less resources.
Weakauras	Commonly used addon for buff/debuff tracking and more.
Aura Frames	CPU friendly alternative to tellmewhen and weakauras.
Damage Meter:
Skada	Commonly used Damage Meter. Is a solid choice.
Details	Feature rich Damage Meter thats relative new but already the best choice.
Nameplates:
Plater Nameplates	Alternative Nameplate addon.
Kui Nameplates	Go-to choice Nameplate addon.
EKPlates	Alternative Nameplate addon with an interesting style.
Raid Tools / Boss Mods:
Deadly Boss Mods	defualt choice for Boss timer and alerts.
Bigwigs Bossmods	CPU friendly alternative to DBM.
Exorsus Raid Tools	Raid tool from one of the strongest compatitive guilds.
Raid Assist	Provides a lot of features for raid organisation.
RCLootCouncil	The best addon to organise the loot in your raid.
Action Bar:
Bartender	default choice for Action bar mods.
Dominos	Alternative Action bar mod that is more CPU friendly.
Unit Frame:
Shadowed Unit Frames	CPU friendly and feature rich unit frame addon.
Z-Perl Unit Frames	Popular unit frame addon.
Grid 2	Popular and CPU friendly raid frame replacement.
Cast Bar
Quartz	CPU friendly Cast bar replacement.
Gnosis	Feature rich Cast bar replacement.
Combat text:
MSBT	Default choice for Combat text display.
All in one:
Elv Ui	Popular Ui replacement with a lot of features.
Others:
Doom Cooldown pulse	Flashes an icon when a cooldown comes up.
TrufiGCD	Provides a time line for your casts. Interesting for streaming.
Gottagofast	Default choice for Mythic plus timer.
Advanced Interface options	Provides a easy to use interface to change Game Cvars.
Garbage protector	Organized the collectgarbage function to improve performance.