I am primarily a Windows user, since at work we have to use Microsoft. 

However, privately I own a MAC Book and I am pretty annoyed with learning new shortcuts all over.

Anyway, below you will find a small list of helpful shortcuts.

Description Shortcut
Quick delete a song in iTunes without confirmation Dialog. Only works in non-smart playlists. Cmd + Alt. + Del.
If you want to permanently delete songs from your library without one mouse click, use this one. Cmd + Del. When you see the annoying confirmation dialog press M. M is the shortcut in the dialog for 'Move to Trash'.
Close the currently opened window, without closing the parent application. E.g. Close a tab in your web browser like Firefox or Safari. Cmd + W
Quit an application. Cmd + Q
Not worth mentioning, but some people might not know yet: Switching between applications. Cmd + Tab
Jump to begin of a line in a text document. Cmd + Left Arrow
Jump to end of a line in a text document. Cmd + Right Arrow
Jump to the beginning of a text document. Cmd + Up Arrow
Jump to the end of a text document. Cmd + Down Arrow
Navigate left or right between words in a text document. Alt. + Left or Right Arrow
Move cursor to / highlight Safari address bar. Cmd + L
Open Key Chain. Cmd + , (Cmd + comma)
Tab through open tabs in a web browser like Safari or Firefox. Annoyingly this does not work for windows in other applications. Ctrl. + TAB (forward) Ctrl. + SHIFT + TAB (backward)
Tab through / Move between windows of one application. MacBook keyboard Cmd + <> Normal keyboard (QUERTZ layout) Cmd + ^ Here is an URL, which will provide you with some more explanation also for US keyboards. https://apple.stackexchange.com/questions/193937/shortcut-for-toggling-between-different-windows-of-same-app If you have windows of an application open in full screen however, you will have to use the Mac OS Mission Control shortcuts, which are ... Ctrl. + Left Arrow Ctrl. + Right Arrow
Show / Hide Desktop F11
Show / Hide Dashboard F12
Show / Hide view for single picture from library in photos app. Space
Force Safari to reload a page ignoring the cache Cmd + Alt. + R
Show page in Safari only text / read mode Cmd + Shift + R