If you are thinking to upgrade easily to Windows 8.1 from Windows 8 DON'T DO IT.....before following these NECESSARY steps. If you have some, just add them to this thread!
1) Uninstall the graphic driver.
It will give for sure problems after the new restart and you will get a black screen. Follow the 3rd started by dacul here Short tip for the blank screen on 8.1 upgrade
2) Uninstall ANY antivirus you could have in your system.
KIS 2013 caused the installation to get stuck at 58% for me. After resetting my system the setup gave up and asked me to repair my previous install. So I had to uninstall it and start the procedure again. Launch setup ONLY if you don't have an antivirus installed. Maybe Windows Defender wouldn't interfere but I haven't tried it.
3) ASMedia XHCI USB3.0 controller will stop working when rebooting. This is caused by the Asus SUITE II and its function AIChargerPlus. It needs to be updated. Follow these instructions to get them working again!
1. open device manager and uninstall both ASMedia XHCI Controllers
2. go to control panel, programs and features, uninstall Asumedia ASM104x USB 3.0 Host Driver
3. go to control panel, programs and features, uninstall AI Suite II, select AIChargerPlus, USB 3.0 Boost, and EPU.
4. Restart the PC.
5. Test your port. If not working, scan for hardware changes in device manger.
6. (optional) re-install USB 3.0 Boost. Do not re-install AIChargerPlus.
4) Punkbaster (anti-cheat utility) will stop working and you will be kicked out from servers (BF3 is affected by this), when you first login after updating to Windows 8.1. Here is the solution:
Go in the Punkbuster folder \Battlefield 3\__Installer\punkbuster\redist and launch pbsvc.exe. It will reinstall it. Reboot and you will be able again to play online!
5) feel free to add your own and verified tips