We will create a more formal instruction set for this, but for now here is what you need to know:
1) The wallet can regenerate all private keys from the wallet root key. So as long as you backup your wallet after you create it your balance is safe (in theory).
2) You should backup the PUBLIC KEY of all unregistered accounts otherwise you will have to scan all transactions with all keys which could take a VERY LONG TIME when the network transaction volume picks up (or if you had a lot of transactions).
For this reason I recommend registering all accounts on the blockchain *or* backing up all public keys for the unregistered accounts you do create.
You can backup by going to File -> Export Wallet which will save a .json file with your wallet contents. The private keys are encrypted with your password. Save this file on a separate disk. If your password is not very strong then do not store it where anyone else can get to it.
Strong wallet passwords are recommended.