Using the SharePoint Central Admin Backup/Restore Utility, perform a full farm backup after each time you make configuration changes to the SharePoint farm. This backup will protect most of the farm configurations.
Schedule an stsadm.exe backup script to run at least daily on each site collection. These backups will protect the site collections and their content.
Create a SQL Server maintenance plan to backup all databases and transaction log filres on a regular schedule. SQL database backups can be also used to recover site collections. SQL backups also protect farm configurations.
To test a full restore, you can first restore the farm using the SharePoint Central Administration Backup/Restore Utility. Next, you can restore each site collection from the latest backups using stsadm.exe. This should get you to to a healthy state, as of the time of your latest site collection backup.
You may also want to test restoring a content database by creating a new web application on the farm, restoring a content database backup in SQL, then running the stsadm.exe command for attaching the content database to the new web application. Run iisreset /noforce then try hitting the restored site collections from the browser.