A new trailer from Bungie and Activision today highlights the Destiny pre-order bonus DLC, the Vanguard Armory. As an incentive for reserving the game ahead of time, the Armory essentially grants early access to some DLC weapons and armor, plus an exclusive emblem to be shown off in-game.
So what does one need to actually do to acquire the Vanguard Armor add-on? Just pre-order from a participating retailer, as these things typically go. The whole "early access" part does seem to imply that the DLC will be released later on to everyone, at least.
For now, you can see a trailer showing off the content. Bear in mind, this is just a pre-order incentive, so reserving any version of Destiny will work. Still, the special Ghost Edition does look really nice.
Something else to consider is the beta access you get for pre-ordering. Bear in mind the beta will begin this week for Xbox 360 and Xbox One, on July 23, and was released earlier this month for PlayStation 3 and PlayStation 4.