Automated

You can use CleanMyMac. It also helps you to uninstall Applications along with removing their residual files:

• Run a system scan and free up space
• Uninstall Applications using CleanMyMac
• Some Applications/Softwares might not be detected completely using CleanMyMac. Example: R

Manual

The key to manually freeing up space, is to figure out where is a sizable portion of your hard disk space getting used up. There are some HDD space visualization softwares which will help you do just that.

Suggestions for HDD Space visualization softwares:

• Disk Inventory X (Free and Open Source)
• DaisyDisk (paid)

Misc

• Homebrew
  • Clean Up Brew. Check size of cleanup using brew cleanup -n and brew cleanup to perform it.
  • Check the size of Cellar (where homebrew installs) by using du -sh /usr/local/Cellar
• Check iMovies files in ~/Movies/iMovie Library. I happened to find 7 GBs just lying there from old resources which I no longer needed :)