My favourite tool for this is Disk Inventory X. It's got a fantastic graphical representation that I am struggling to describe using text. But basically it uses colour coded blocks - different colours for different types of data - and those blocks are sized according to how big the file or folder is. You can hover the mouse pointer over each block to find out the path/filename of the offending file. You can see instantly at a glance, what the biggest space hogs are. At least take a look at their web page so you can see what I mean about the user interface. It's free and I find it invaluable.
Download / read more here: http://www.derlien.com
Also, if you have an iPhone, iPod Touch or iPad, then check your iTunes sync settings - you will probably find that your iPhone (for example) gets backed up to your computer every time you sync it. I have an iPad Mini and an iPhone 5S - I see four subfolders under ~/Library/Application Support/MobileSync/Backup
and they are about 15GB each.
To check for yourself, press Shift+Cmd+G while you're in Finder, and enter the folder name ~/Library/Application Support/MobileSync
. Highlight the folder Backup
then press Space to bring up the Quickview window (which will tell you the total size of the Backup folder).
du -s *|sort -n | tail -10
is your friend.sudo tmutil disablelocal
. I found my CPU use would randomly skyrocket when creating a local backup, so it will save battery as well. Finally, check that you don't have any updates that haven't been installed; they download in the background and take up space.