Yes its a big tasks for DBA's, when you do df -k in solaris and see your mount points are reaching 100%. It difficult to find what to delete for what to compress. I usually try some commands mentioned below :
This command will list top 10 directory from parent directory
du -ks * sort -rn head -10
This command will list out all files greater than mentioned size.
find . -size +10240
Keep Troubleshooting !!!