From top to bottom:

HoTT

Casting timer (useful to watch if your slow-casting spell will land before the target dies)

Extra-large target health bar with percent

Consider color just below it

Target name in largest possible size (font 10)

Buff icons (same size icons as the default UI)

First 14 buffs are centered under the target, the next 14 in the lower right corner. That's more than enough for PCs and group targets, but on raids...

Next 14 go to the upper right corner, then 14 in the upper left corner, then 14 in the lower left corner. Only if you get more than 70 buffs on your target will it start to show buffs over the target name.

Since it's transparent I've included a faint outline around the edge, so you know where not to click. You can change the color of it (right click, then choose background tint color). I usually leave mine black but it also looks good in red, white, or purple.