Take out my magnifying glass, inspect every square nanometer of it to make sure its flawless and that Santa's elves (Foxconn workers) aren't letting their standards slip.
Then I'll fire it up, take a look at the screen, inspect for dead pixels. To achieve this, I will fire up a series of super fast colour switching screens which will likely give my dog a seizure while rendering my eyes full of blood.
If I find one dead pixel, I will stomp my feet on the ground - careful to avoid my seizing dog and then call Apple to setup a return and buy another one.
If there are no dead pixels, and my dog is still alive, then I test for light leaks. To do this I shine a flashlight at the screen for 10 minutes, then turn off the lights -- oh wait, that's the glow in the dark test, I'm getting ahead of myself.
Where was I again?