How to upgrade and debug broken packages

The 9-11 version is very stable but sometimes problems pop up with backports as happened recently with the Audacious package. To start, query the package database to see what versions are in the configured repositories:
apt-cache show audacious

Looks like the www.deb-multimedia.org version is 3.6 so we need to delete the most recent:
sudo apt remove audacious

Then get the right one:
sudo apt install libaudcore3=3.6.1-dmo1 audacious=3.6.1-dmo1

And finally lock the package so we can upgrade in the future without problems:
sudo apt-mark hold audacious
sudo apt update
sudo apt upgrade

For the 9-11 version you should:
sudo apt-mark hold locales
sudo apt update
sudo apt upgrade

Periodically you should also:
sudo apt-get autoremove
sudo apt-get clean
to free space on your SD card.

NOTE: new users only need to do the commands in red to a "clean" image.