Personally, I would skip the cleaning and sanitizing of a new glass carboy, and instead travel back in time and not buy one in the first place. Using a glass carboy is like holding a bomb with a lit fuse.
If you must use it, it just needs a quick rinse before sanitizing. There is no crud in it since it's new, and so there is no need for soaking with a cleaner. They are very slippery when wet, especially when PBW is involved, so be extremely careful.