I know a lot of people use the npcscan addon, thats nothing new. the problem with npcscan is that even when it detects a rare spawn you still need to find it. depending on the mob this can be quite dificult but using a Focusing Lens makes it extremely easier. a Focusing Lens will face you in the direction of the target and light it up making it very easy to find. it has a 60 yard range and doesnt require line of site. it doesnt matter if you use Dark Jade Focusing Lens, Shadow Crystal Focusing Lens or Shadow Jade Focusing Lens, they all do the same thing.
i should probably also add that the lenses are channeled so you can't use them while moving or falling.
if you are after one of the flying rares in storm peaks (eg Time-Lost Proto Drake) then you should carry some Snowfall Lager so you can pull/tag him easier without worrying about falling to your death after.
a couple of people who gave me +Rep mentioned that they didn't know about npc scan, so to those people i would also recomend getting npcscan overlay, it shows on your map where npcs patrol and updates to only show npcs currently being tracked by npcscan. it helps a lot if you are after a specific rare but it can also be helpful to quickly check if rare is near during normal travel (eg flying along the patrol path of Putridus the Ancient while doing argent tournament dailies)