Tricks for mounting a rod vertically so it's perfectly perpendicular

Hi, I'm relatively new to this whole DIY thing. I"m trying to mount two closet maid shelf tracks vertically, so I can hang shelves on it. I'm wondering if there are any tricks for mounting a rod vertically, and making sure that it's perfectly perpendicular relative to the wall? If I were mounting this horizontally, I"d just screw it in with one screw, put a level on top of the track, rotate it until the level says it's good. But I'm not sure what's the easiest way to do that when I"m mounting the rod vertically. I suppose I could use a command strip to attach the level to the side of the rod. But is there an easier way? Thanks.