Preparation

For debian-based system: Install “debfoster” and run it. After answering a lot of questions about your packages you will have a system without unnecessary packages and a short list of only the packages that you have actively chosen to install. (Tip by Motin)

Another way to clean the system is:

 $ apt-get autoremove

To Backup

 $ dpkg --get-selections

To Restore

Importing the List:

 $ dpkg --set-selections < /backup/installed-software.log

Install the imported list:

 $ dselect