How do I know how to describe my position on the airport when I contact ATC? When asking for taxi clearance, a pilot must include his location when contacting ATC. However, I'm not quite sure exactly how to state your position in the airport. 

For example, I've heard some pilots say something such as "Ground, N123DB is southside by the tower, requesting taxi clearance," but I've also heard something like "Ground, N123DB is at transient parking, requesting taxi clearance." How do you know your location in the airport? 

Obviously, I can look at an airport diagram and find out where I am, but how do I communicate this using proper terminology to ATC? Is it standardized?
There isn't really an official protocol, beyond the conventions everybody uses out of habit.  Just pick the most prominent landmark, building or chart-labeled zone you can find or think of.  The controller knows all of them so as long as it's not something like "next to a light pole", he/she will figure it out, and if not, they'll ask for clarification. 

If the airport has an area designated "transient parking" on the airport chart, use that.  If you're on a ramp area close to the entrance to taxiway Alpha, you could say "xxxx on the ramp near Alpha".  If you're on a ramp in the hinterland somewhere near some hangars, pick the nearest building with a business name associated with it, like "xxxx by Standard Aviation...", or "xxxx by the Shell fuel pumps", whatever.  Use common sense and don't overthink it.