I have all the really important stuff right in the middle for easy review. As information becomes less important for my immediate attention it is pushed away from the middle.
The center of my screen is dominated by ICE Hud and Deadly Boss Mobs.
DBM gives me lots of information in my chat window. I run prat which provides the timestamps as well as the level and class coloring for normal chat. I also black out the background so it is easily readable regardless of what's behind it.
All my primary attacks are here with bartender and they are keybound to keys I can easily use with my left hand since I drive with my mouse. I also have Dr Damage which puts the average attack value of each ability on the keybind.
The last portion here is DoTimer for my cooldowns. If I need to know exactly how long until I can use an ability I only have to look down to the left from all the action.
The bottom right has more info from DoTimer, Bartender, and includes recount.Here I see my buffs and timers for the debuffs I have on my targets. Once again if I look here I will notice I do not have Blood Plauge on my target, but I have 15 seconds left on frost fever. My cursor was apparently over one of my raidmembers but it shows down in the corner where I don't have to make an active decision.
You can also see DBM has started the enrage timer since it was getting close. As the countdown closes in on zero seconds the warning moves towards center.Recount is also down in the corner since I don't make decisions using it while in combat. I'm sure you know by now I like reviewing recount data after raids to decide what is working for me and what isn't.
The last part of my screen I really want to draw attention to is the upper left. I use AG Unit Frames to see the health, or living status, of everyone in the raid. I also have my FPS, latency, and durability displayed here.
I believe it is AG Unit frames that is also putting the heals and damages on each member. To be honest, I only glance at this to see who is alive and who is dead. In 5 mans the frames are configured to show mana so I know when to slow down on my chain pulls.
The top center just has the unit frame for my targeted mob. I primarily have this so I can inspect players when I target them.
The top right has my mini map and shows all my buffs. The only buff I look to find during combat is Horn of Winter. In a 25 man raid I don't even bother. I was one of 3 DK's and I know the DPS DK's will keep that up at all times to increase their position on the damage meters.
With this layout I can get the information I need while in combat by looking at my toon, or down to the right or left. I don't have to go hunting all over my screen to find something important. I'm told by ergonomic engineers this speeds my reaction times and slows the onset of fatigue.