if you have been using your tablet for email, try pruning old emails with attachments as these eat up a lot of space

check what's in /home/user/MyDocs/ - the directories under there are "hidden" with a dot. you might have a load of mp3s etc. I have moved these directories to my SD card and replaced them with symlinks, e.g.

cd /home/user/MyDocs
mv .images /media/internal/images
ln -s /media/internal/images .images

and so on