It's recommended that you make a backup copy once a week. look for the wallet.dat file in your C:\Users\your user name\AppData\Roaming then look in the wallet folder that you want to backup. Copy the wallet.dat file to a usb drive just make sure to rename after it reaches it's destination (if you are backing up multiple wallets on same usb drive) so you know what wallet it belongs to. Then if you do have a HD failure you simply redownload the wallet take your wallet.dat file from your usb drive and replace it with the one that is in the wallet folder. (don't forget to change name back to wallet.dat). Close wallet, reopen wallet, let it sync and you are done.
Cheers