I finally got my Lumia 925 to update after trying 5 times and getting the 80188308 error. Here's what I did:
1. Backed up my texts and settings, copied pictures and music to my PC via usb.
2. Used Nokia Recovery Tool to downgrade to 8.0
3. Downloaded Preview for Developers app then upgraded to 8.1
4. Tried 8.1 Update 1 again...and SUCCESS 1ST ATTEMPT! :smile:
5. Hard reset phone and restored backup, copied pictures and music back to phone from PC. :grin:
Not sure if this will work for anyone else but if it does, great! Good luck everyone!