It doesn't really matter; both ends have targets to center -- the home button on bottom, the sensor portals on top, especially if it's a full-coverage protector with faux fascia for the 6 models.
For skilled, experienced hands, a free form placement should be no problem.
The "hinge" method adds a helping hand, but beware of the misalignment that can occur from the amount of tension or slack on the tape. Test it before committing, to see that the "hinges" are solid and everything is aligned.
Anker's button nub guides you 95% of the way there, but it still requires a vigilant placement. If it were me, I'd have done it the other way around, and have a temporary nub to stick on the home button, not the protector, so you can see what's happening as you lower the protector.
Some protectors include an alignment tray, or the Belkin contraption used in Apple stores.
To me, an air duster is essential in getting the last bit of stray dust off the screen right before application.
I've tried the steamy bathroom environment, but I'm not sure it actually made a discernible difference. If anything it might have been worse.