Show the biggest files with their size in the file system or in a certain folder.
The 10 biggest files in the whole file system:
sudo du -a / | sort -n -r | head -n 10
The last number (-n 10) sets how many of the biggest files should be shown.
The 10 bigges files in a certain folder:
sudo du -a /home/ | sort -n -r | head -n 10
Here the home folder as an example.