As I am cleaning up my backup drive as step 1 in a long series of recovery steps, I want to post a plug for this wonderfully-useful piece of software: "filelight" that makes this MUCH easier.
This is a great (and fast, even on huge multi-TB drives!) way to visualize what is taking up space on your filesystems, and thus prioritize what to clean up.
Available in standard Linux distributions, but here's the upstream link:
@TerryHancock GNOME's Disk Usage Analyzer (baobab) works nice.
