I know a lot of people who have switched to the Mac in the last few years and while most them are already very knowledgeable OS X users, I occasionally get usage questions that make me realize there are a few small tips that everyone should know and that a lot of people don't. I've compiled a few here in hopes they might come in handy.
⌘` or, "Move Focus to Next Window in Application"
This is an extremely useful keyboard shortcut. By default, on a US keyboard, it's command-backtick (`) and it will cycle through all the windows of the current application. Think of it as command-tab for the current app. You use tab to go between all apps and backtick to go between all windows of the current app.
I'm always surprised by how few people know about this shortcut. And, like all other default OS X shortcuts, you can change this in the keyboard pane of System Preferences.
Finding your current location
When you're writing a document in TextEdit or browsing a few levels deep in Finder and you quickly want to find out where you are, you can command-click on the window's title to get a menu showing your current location and a hierarchy back to root. This doesn't work in all applications, but most of the time if you expect it to, it does.
And, of course, clicking on any item in that menu will open that directory in Finder.
In addition, many people don't know about the path combo button available in Finder window toolbars. To add it, customize the toolbar and drag the Path button over. Clicking that will show you your current location back to the root from any window.
Flush DNS
This probably doesn't come up for most people, but if you're in a large network or you do your own hosting or you change DNS more than a few times, you've definitely needed to flush the DNS cache on your Mac once or twice. Easiest way:
lookupd -flushcache
Depending on your rights, you might need to run this with sudo.
Easily uninstall preference panes
If you're like me, you try new applications and preference panes all the time, which means occasionally you need to do a bit of house cleaning and remove older things you don't use. For applications, I use AppZapper, but for preference panes even easier. Simply open System Preferences and right- or control-click on an icon in the "Other" section and you'll be given an option to remove the pane. Done and done.
Get combined info
Occasionally, you might want to select 15 files and find out their collective filesize. I've actually witnessed people select files, get info, and quickly add the values from each of the 15 panels that pop up. Madness! Here's a much quicker way:
Select your files and use option-command-i (⌥⌘i) instead of just command-i. This will open a single panel with combined details. You can also get this from the contextual menu by right- or control-clicking on a group of files and then holding down the option key. "Get Info" will change to "Show Inspector" and you can click that for the same effect.