Below are some wonderful shortcuts and tricks when using macOS that have really changed my life.

Shortcuts

Audio Vision

Controlling Display and Audio Settings

Shortcut Function
⌥ volume Open Sound Preferences
⇧ ⌘ volume Fine Volume Control
⌥ 🔅 Open Display Preferences
⇧ ⌘ 🔅 Fine Brightness Control

Power

Sleep and Power shortcuts. For MacBooks without ⏏️, user the power button instead

Shortcut Function
^ ⏏️ Shut Down dialog
^ ⌥ ⌘ ⏏️ Shut Down
⌥ ⌘ ⏏️ Sleep Computer
^ ⇧ ⏏️ Sleep Display
^ ⌘ ⏏️ Restart

Moving around Finder and App Windows

Shortcut Function
⇧ ⌘ . Show Hidden Files
⇧ ⌘ / Go To Help Menu
⌘ \` / ⌘ < Cycle Windows
⌘ ⇥ Cycle Apps
⌘ ⇥, ↑ Select Window of App

Miscellaneous

Everything else

Shortcut Function
^ ⌘ D Dictionary Definition