Tomorrow is the scheduled launch of iOS 8. If you are upgrading an existing device, here are some tips to make it easier and safer. If you are getting a new iPhone on the 19th, then I think these are even more important.
Delete every app you haven't used in 3-6 months. You can install them when you need them but every app slows down the migration to a new device. You also reduce the chances you will have a power-hungry backgrounding app you don't really want.
Turn on encrypted backups in iTunes. Encrypted backups retain most of your passwords and it saves a ton of time.
Backup to iTunes. An iTunes backup restores much faster than iCloud.
Use something like iExplorer to download any voicemail, text message logs or whatever you think you want to keep. Prepare for the worst case scenario.
Doing all of this stuff takes about an hour. Not doing it may take several days.