iOS 7 releases tomorrow. If you have an iPhone 4 or newer, an iPad 2 or better or a 5th Generation iPod Touch you're eligible to update. (Full specs on Apple's site). Historically, Apple releases these updates around 10 a.m. Pacific/1 p.m. Eastern.
As with any major update, it is my strong suggestion that you make sure you have good backups of your devices prior to applying the update. If you are tech support for your friends and family, encourage them to do the same. Since many of us will be at work when the update is released and tempted to upgrade while we're away from home, taking some time to back up the night before or the morning of the release is a good idea.
If something goes wrong, or if you choose to erase your iOS device and perform a full restore the easiest and fastest way to do so is by tethering to a computer. While you can restore from iCloud, and I have successfully done so a couple of times, but you'll find restoring from a computer backup a lot faster, especially considering Apple's servers are going to be slammed tomorrow. For this reason, I recommend you top up your iCloud backup immediately before applying the iOS update as well as perform a full backup to your computer the evening or morning before. It's also a good idea to take this opportunity to make sure all your Apps are up to date. There will be a rush of App updates over the next few days.
Keep in mind once you switch on iCloud backups, your Mac will stop making backups of your iOS device by default, but you can always run a manual backup by connecting your device and clicking the backup now button in iTunes. Note, if you want all your stored passwords to be restored, make sure you select the option to encrypt your backup in iTunes.