Apple offers two ways to move your content from one iPad to another: iCloud or iTunes. To use the iCloud method, you need to be running at least iOS 5, have an iCloud account and be connected to a wireless network with the iPad plugged into its charger. You can turn on iCloud by tapping the Settings icon from the iPad's Home screen, and then select iCloud. The option for turning on iCloud Backup is in the Storage & Backup area; you get 5 gigabytes of storage free and can buy more from Apple if needed.
Once you have backed up the older iPad's settings and content to iCloud, turn on the new iPad Air and go through the setup screens, where you will get an option to restore the data from a previous iCloud backup. Once you log in with your iCloud (Apple ID) name and password, you can download the backup to the iPad Air.
With the iTunes method, start with backing up the old iPad's contents to the computer. Connect the two devices with the iPad's USB cable (or sync with iTunes over a Wi-Fi connection). When the iPad icon appears in iTunes, click the Summary tab and then click the Back Up Now button. When the backup is finished, connect the iPad Air to the computer with the USB cable and choose the option in the iTunes window to restore the iPad from the previous backup.
Transferring your prepaid cellular data account depends on your carrier. Some let you move it yourself when you go to Cellular Data in Settings and log into your account with your previous user name and password.