I covered the fundamentals above. You need to ask specific questions as needed.
1) Use the Backup Project option to backup the project data files, accents and filters. Manage exhibits outside of TMG.
^^^ This is the critical backup and should be done every TMG work session. ^^^
2) If you do a test project restore, do it to an empty folder. There is no need to disturb an existing project to test a backup.
3) Use the Backup Customizations option to back up everything else. (You should't need to do this type of backup very often.)
4) Only back up those customizations that you add or edit. There is no point to back up customizations that are added by the program installer.
5) Do not restore the Preferences > Program Options customization (the app.ini file) to computers other than the one on which the backup was made. (You could make a customizations backup on each different computer.)
6) You don't want to restore the Preferences > Program Options customization on a newer version of TMG (although this issue is moot since there won't be a new version of TMG).
7) Lastly... Copy your backups off of your computer and store copies elsewhere... on a second computer, on a CD or DVD, in the cloud, at another person's house or at your worksite). You could even use USB flash drives but use two and alternate them. Make GEDCOMs. Print your data. Think about the disasters that might happen and plan ahead.