Assuming that you use Raspbian, if you’re not using libreoffice, wolfram, or scratch, removing them can save a lot of space.

sudo apt-get purge libreoffice wolfram-engine sonic-pi scratch

Remove the junk and temporary files by removing old package dependencies and junk produced by apt-get.

sudo apt-get clean
sudo apt-get autoremove

Find your 10 largest directories:

du -h | sort -nr | head -n 10