How to backup before installing iOS 7?

You wanna go into iTunes and do Backup to computer.

Don't do iCloud backup, because it will corrupt when you try to restore OSes.

connect ipad on your pc, then it will automatically sync. For assurance, go to iphone then choose backup. That's it make sure to double check the backup date and time

Certain games, like Angry Birds recently, got the ability to sync your progress to a self-made online account (like the Rovio account for Angry Birds) which let you transfer your progress easily to other devices. For those games you don't even need to back-up at all. If not every game you would like to keep progress from has this ability, I too would suggest using iTunes to perform the full back-up.