Go to your "My Documents\My Games\FINAL FANTASY XIV A Realm Reborn" directory, find the folder of the character whose UI you would like to copy (it'll just be named something like CHAR_40000blahblahblah so good luck if you have multiple characters) and copy all 10 of the .DAT files inside into your additional character directories, overwriting the files already there. That will copy your UI, character settings, keybinding, camera settings, pretty much everything.