Quick Look
One of the simplest tricks on Mac is press Spacebar to preview files. It works on a surprisingly large variety of file formats: office docs, PDFs, audio files, video files, fonts, etc. Saves a lot of time.
Spotlight
Cmd + Spacebar is the shortcut to Spotlight search which you can use to quickly open apps or files. This is a very simple and well-known feature and one of my most used keyboard shortcuts on the Mac. Spotlight can also perform calculations and look up other useful info like current conversion rates for currencies, the weather and flight statuses.
Digitally Sign PDFs with Preview
Preview app can automatically create a digital signature to allow you to digitally sign PDFs. Go to Preview, Tools, Annotate, Signature, Manage Signatures. Then hold up a signed piece of paper to the webcam and it will automatically create and save that digital signature for you so you can use anytime you need to digitally sign a PDF in the future.
Emoji Keyboard
To bring up the emoji keyboard in Mac OS simply press ctrl+Cmd+space
Quickly hide or close apps
Hold Cmd while pressing tab to scroll through your open apps. When you reach the app you want to close or hide, press either Q to quit or H to hide the app.
Dictation
MacOS has a built-in speech to text feature called Dictation. Instead of typing, just press the fn key twice and a microphone icon will pop up and then you can start speaking into your microphone and it will type out what you’re talking and when you’re done you just click Done.
Screenshots
Cmd + shift + 4 = Capture dragged area & save to desktop
Cmd + shift + 3 = Capture entire screen & save to desktop
Cmd + ctrl + shift + 3 = Capture entire screen & copy to clipboard
Cmd + ctrl + shift + 4 = Capture dragged area & copy to clipboard
Cmd + shift + 4 + Space = Capture a window & save to desktop
Cmd + ctrl + shift + 4 + Space = Capture a window & copy to clipboard
Quickly create file from selected text
Select text then drag and drop to desktop or folder and it will automatically create a file with the selected text in it
Precise Volume/Brightness Control
Hold Shift + Option and change your brightness or volume to adjust in smaller increments for more precise control.
Summarize Text
Mac OS allows you to quickly summarize long pieces of text in just a few seconds. To summarize a text first select it, right click on the selection and click on “Summarize”. To enable the summary feature, click on the app name in the status bar, click Services, Services Preferences, scroll down and check “Summarize”.
More Space
If you own a Mac with a Retina display you can scale the screen to create more screen space. This feature also works if you have a second monitor connected to your main Retina device. Go to System preferences, Display, Click Scale, and choose More Space.
Quick Dictionary
If you have a Trackpad you can select a word and do a 3-finger tap to quickly bring up the definition of the selected word.