I love these various shortcuts. Most are somewhat obscure, or at least were to me.
To open Quick Look in full screen mode
To open a new Finder window (with no other finder windows open.) Hold down Command and Command + Tab until you get to the Finder. Once the Finder is highlighted, and with Command still held down, hold the Option key and then release the Command key. It’s easier than I make it sound. This will also work in other Apple apps, but if there are existing windows, it will take you to them rather than create new ones.
press Command - Tab to Finder - press Option - release Command
In Finder, to go to a specific path (Tab Completion works here too.)
In Safari, Mail, and probably most Apple apps, you can lookup a word in the built in Dictionary.
In Terminal, if you hold the Option key, your cursor will turn into a small cross. You can then place your cursor anywhere in the command line. This is a great feature.
This isn’t a keyboard shortcut, but it is quite handy. To open a man page in preview.
man -t bash | open -f -a /Applications/Preview.app
Go forth and prosper with your newfound knowledge..