I know this is going to be old hat to some of you, but so what? This is about things I'm learning and/or that I think may help others learn about faster than I did.
Patch 3.0.2 brought focus frames, long a staple of many UI-modifying addons, into the stock user interface. Focus is essentially a secondary target, something you mark and can then target for all the usual sorts of things - shooting, hitting, casting, healing, etc. - without losing your primary target. The ability to select focus targets and then do stuff to them has always been there, available for macros and addons and directly issued slash commands, but invisible.
Now it's visible. You select your target, right-click, and there's Set Focus as an option. Voila! Its own little frame...which you can right-click to unlock and move it around. Here's what I'm doing with it at the moment:
In the upper left, Tivara's legs and her bright red and black boots. In the middle, the focus frame, moved to right above my action bars. In lower right, the aforementioned action bars.
The red circle marks Misdirect, with 5 seconds remaining on its cooldown. (That great big number comes courtesy of OmniCC, which I recommend even to people who generally avoid addons.) At the moment I took this screen shot I wasn't in a fight. At the start of a pull, I'd click Misdirect and then the frame for the tank - in this case, our fine huge bull orc Gargantax, whom you can't have because we love him. He's got Misdirect, I switch to the first pull target, put up Hunter's Mark, and my pet and I go to work. After Misdirect has cooled down again, I put my right hand over on the mouse and repeat the pair of clicks, while my left hand keeps up Serpent Stinging and Steady Shotting (or whatever it is I'm doing, depending on the enemy), then bring my right hand back to the keyboard. Gargantax gets extra threat, I get a bit less, and my routine isn't disrupted.
Now, you may not have ergonomic preferences anything like mine. I find that I am at my most responsive and productive when I mostly stay on the keyboard, but throw in mouse action from time to time. If you've never thought about your preferences, this is as good a time as any, too. :) Do whatever is handy for you to make your focus frame as accessible and convenient for you as my setup is for me and then use it a lot. Your groups will benefit. It's a hunter treat for the rest of them!