Step 2
Backup your device and do a transfer purchases.
Transfer Purchases
In iTunes 12 they moved "Transfer Purchases" to the [ File ] Menu
[ File ] -> [ Devices ] -> [ Transfer Purchases ]
Backup
This will create backup of your all your data/pictures this will NOT backup your sync'ed music as it should already be in iTunes. If you purchased the music through iTunes on your iphone/ipad it will be backed up through Transfer Purchases in the previous mini step. BACKUP TO THIS COMPUTER! DO NOT BACKUP TO ICLOUD. iCloud has a 5gb limit and all sorts of other issues.
AGAIN
DO NOT USE ICLOUD BACKUP!
If you have never jailbroken before you are pretty much ready to go. All your text messages, phone numbers, camera pictures, data for majority of your apps are now safely backed up on your computer.
If you had PREVIOUSLY jailbroken your phone and have music and videos you downloaded from things like Grooveshark and Music Box then the next step is for you.