First you need to select a backup location. I use a separate hard drive and have a folder there named "TDU Backups".
I keep a shortcut on my desktop to both my original savegame folder and my backup folder.
Each night after playing TDU, I open both folders then drag and drop my original savegame folder to my backup folder. Pretty simple.
Additionally, I also keep 3 days worth of backups just in case something happens and one backup doesn't work for some reason (it's never failed, but ya never know).
Example:
21 Feb 09 Backup
22 Feb 09 backup
23 Feb 09 Backup
When I make the backup for 24 Feb, I'll rename the 21 Feb to 24 Feb and just continue rotating the dates.
For the upmost in security, I suggest making periodic backups to a rewriteable CD or DVD should you experience a hard drive failure.
I'll also make a special backup folder for when I try something new like a road mod, a sound mod, or a car mod and name the folder "backup before car mod" (as an example).
Also, be sure that if you try any mods on the game to make a backup of those original files that you'll be modifying, like vehicles, or rims, weather, etc.
Sounds like a lot of backups but it doesn't take but a minute to do it and it'll save a lot of heartache if something goes wrong.
Hope this helps.