A quick way of showing which directories are taking up how much space on unix systems.
Starting at the root, use
du to show disk usage.
cd / du -h --max-depth=1
-h makes the output human-readable, and
du form descending into subdirectories.
You should get output that looks something like this:
6.2M ./sbin 8.0K ./home 232M ./opt 4.0K ./boot 4.0K ./mnt 5.2M ./bin 8.0G ./var 0 ./sys 4.0K ./media 80M ./root 6.7M ./tmp 1.3G ./usr 120K ./build 4.0K ./srv 12K ./dev 8.9M ./etc
var and to a lesser extent
usr are hogging disk space. Then just
var and run
du -h --max-depth=1 again to see which subdirectories are largest. Repeat.