TapNoiseThe app’s menu bar is a good shortcut reference because it shows commands for the app you are actually using. Learn the actions you repeat, rather than memorising a large generic list.
Decode a few symbols
Command is ⌘, Option is ⌥, Control is ⌃ and Shift is ⇧. A shortcut combines its modifier keys with the final key shown. Hold the modifiers, press the final key, then release.
Open a menu and find an action you perform often. Try it on a harmless document, then use it again in your next real task. Two useful actions learned in context are easier to retain than twenty disconnected combinations.
Read the command’s state
A greyed-out menu item means the action is currently unavailable. A command may need selected text, a particular file type or an active document. Do not troubleshoot the keyboard until that state makes sense.
Shortcuts can vary by app and input source. The menu is a better guide than assuming that a combination from another editor applies everywhere.
Use a sheet when helpful
TapNoise’s shortcut cheat sheet opens when you hold Command by itself and reads the front app’s menus. It needs optional Accessibility permission and will not reveal commands that an app never puts in its menus.
If an important menu action has no convenient shortcut, try adding an App Shortcut. Keep it specific enough that it does not disturb familiar actions in other apps.
Sources: Apple’s shortcut introduction, TapNoise shortcut sheet.