The easiest way to protect your data on any computer is to separate it from the operating system. So if your computer comes with a massive 500GB drive and it's all allocated to Windows or Linux then a failure of the OS could mean that you loose data if you have to do a restoration of the system.

I prefer to use a Disk Partition Creation software that can divide a drive into multiple partitions. At the least two and better three partitions are useful.

On a windows PC with a 500GB drive, this would be a C: Drive of about 150GB, a D: drive of about 300GB and the remaining space to a backup E: drive for keeping copies of files near to hand.

Sadly Windows does not readily give you the ability to re-partiton drives so you'd have to use a thrid party tool like Partition Master (Free) or similar.

Once you have the drive partitioned, you can make the D: drive represent your My Documents by moving it's location, right click My Documents and select Move. Then all you personal files will be stored on the D: drive.

Should you need to reinstall Windows, you can do this straight to the C: drive without the worry of overwriting your files.

Use the E: drive as a place to manually copy files like Word Processor and Graphics to so you have a backup if you accidentally delete or damage a file. You could also schedule Windows Backup to back the files up automatically once a week.

I would also recommend using a Disk Image program like Acronis True Image, this enables you to take backup copies of the whole partition C: and or D: and place that copy either in the E: drive or an external drive. Replacing a faulty Windows by overwriting it with a known good Image Copy is far quicker and easier than doing a reinstall of the OS manually.