It's really simple for me. I started with an iOS 7 device, and made a backup. On the day of the GM being announced, I DL the FW from Apple Developer Portal and install it. I generally will then set up that iOS device as a New Device and start completely fresh.
I've at least one BT keyboard handy, such as my Logitech K811, and I'll pair it with the newly-restored iPhone - then set up my iOS device from scratch. If I'm feeling brave, I'll use the last iOS 7 backup to restore from - since I don't really know how Apple gets settings/apps restored across iOS platforms, starting from scratch seems like the best approach for me.
I carry two iPhone 5s - my daily driver and my iOS test mule. I'll use my test mule first, to see if it blows up. With a new OS (non-beta), I'll load my test mule as I like it, try it for a few days, back it up if it works well, then install the new OS on my daily driver and restore it from the back up of my test mule.
If you're using only one iPhone or iPad, I would just start from scratch once the GM is made available, and set up the device as you like it. I do the same thing with my Macs. What I see being different in iOS 8 - is the new iCloud metadata metaphor - how storage, photos, and such are being handled. I have NOT upgraded to iCloud Drive as IMO it seems to be a moving target.
IMO there are people that want this move to the next platform nailed down. After beta testing for 20-odd years, I've opted to start fresh when a new iteration comes out - and that includes the GM. Or, have a couple of drinks, if that suits you. If you install a beta FM, assume you will keep nothing when the next version comes out and start with a clean slate - which is what's worked for me recently. Until it doesn't. YMMV.