Here's my layout:
Basically I have the following:
MP and MP bars enlarged and in the center, underneath my character.
Target HP bar just above my HP and MP bars, so my eyes don't have to jump to the top of the screen to see.
My buffs and debuffs are to the left of center, and right-justified.
Target buffs and debuffs are to the right of center, and left-justified.
Cast bars just above HP/MP bars. Target cast bar is enlarged.
Job-specific gauges to the right of my HP/MP bars.
Information I don't typically need in the heat of battle (As a non-healer) is on the edges and corners.
The cross hotbar is disabled, as I play with a mouse and keyboard.