Interface
As of Midnight prepatch, you won’t require as many addons as before. The most famous addon Weakauras is not working, BigWigs and Details are no longer mandatory addons since Blizzard developed their own, built into the game. You can still download numerous addons to skin textures and make certain elements of the UI look better, but like I mentioned earlier, they are not mandatory.
BigWigs - If you prefer boss alerts in the form of bars instead of a timeline, you can download BigWigs to reskin them.
Details! - If you prefer a cleaner look of the damage meters, you can download this addon to reskin it.
Elvui - another UI replacement that overhauls the default Blizzard UI, from unit frames, damage meters to the Cooldown Manager.
Targeted Spells - In my opinion a must have for high M+. Having the ability to see whether you are being targeted by a spell or ability in a big pack which can one shot you is very important.
Macros
Blizzard Cursor Macro
This macro removes the green circle you would typically have and lets you cast Blizzard at your cursor, essentially saving you time.
#showtooltip
/cast [@cursor] blizzard
Macro for Stop Casting and Use Ice Block
Pressing this Macro Twice will cancel Ice Block to get out of Block Quickly.
#showtooltip
/stopcasting
/cast Ice Block
/cancelaura Ice Block
Be careful to not Press it twice too fast otherwise you will end up wasting Ice Block.
Macro for Counter Spell Your Focus Target
This Macro is essential for Mythic+. It lets you Counter Spell your Focus Target.
/cast [target=focus] Counterspell
Mouseover Focus Target Macro
Another Useful Macro to have is a Mouseover Focus Target.
/focus [target=mouseover]
It is extremely Important in Mythic+ Since it’s a fast paced gameplay and you don’t want to lose time right clicking on the mob frame to create a focus, with that macro you will mouse over the Target you wish to focus so you will know when you need to kick an important cast!
Macro for Mouseover Decurse
Useful for some Keys such as 2nd boss on Halls of Atonement and Sylvanas Mythic.
#showtooltip
/use [@mouseover,help,exists][] Remove Curse