Step 1. Open the Bitcoin client, make sure the client must have the blockchain fully synchronized.

Step 2. If your wallet.dat file is not encrypted by the Bitcoin program anyone who can access an unencrypted wallet.dat can easily steal all of your coins. We strongly recommend you to encrypt your bitcoin wallet in QT clients setting.

Bitcoin Wallet Encryption

Step 3. Now Close your client and locate your Bitcoin wallet.dat

    Locating Wallet.dat / Blockchain in Windows : 

    (Windows XP)

C:\Documents and Settings\YourUserName\Application data\Bitcoin

    (Windows Vista, Windows 7 and Windows 8)

C:\Users\YourUserName\Appdata\Roaming\Bitcoin

    Locating Wallet.dat / Blockchain in Mac OS :

~/Library/Application Support/Bitcoin/

    Locating Wallet.dat / Blockchain in Linux :

~/.bitcoin/

Step 4. Copy / Save your wallet.dat and entire bitcoin folder on external hard disk.

You can add another layer of security by including encryption to most important “wallet.dat” file.