Apple will start selling the on-an-Atkins-diet iPad Air Friday. And with the reviews positively gushing — perhaps an understatement, with powerhouses like the Wall Street Journal’s Walt Mossberg calling it the “best tablet I’ve ever reviewed” — consumer competition might get heated. How can you get one? Let’s count the ways. Stand in line. How 2007. Or 2010. But hey, knock yourself out. Apple’s retail stores will open at 8 a.m. local time on Friday, just as they did the day the iPhone 5S and 5C went on sale in September. Set the alarm clock, Part 1. Apple’s online store will begin taking orders at 12:01 a.m. PT, 3:01 a.m. ET. Steer for this page, pick your iPad poison and click through. Apple warned Wall Street on Monday that the also-new Retina-equipped iPad Mini, which is slated to ship later next month, may be in short supply, but said nothing similar about the iPad Air.