There are just two simple rules:
1. Make DNN backups regularly. Once a month is reasonable for sites that don't change often, and don't include user contributed content or user registrations.
2. NEVER do an upgrade, install a module, or do extensive modifications to a site without having made a current backup.
I mention this after several weeks of working with a site that had problems and the owner attempted to upgrade to DNN8 in an effort to solve the problem. There are several problems with that approach. Naturally, the upgrade failed, leaving a dead site, partially upgraded, and I'm still trying to find a way to do the upgrade successfully.
You have been warned!