When you field strip the pistol, set the slide aside and grab the frame.
At the rear of the frame, you'll be able to see the fixed ejector(pointy thing that sits higher than the rails,) and several metal parts to the right of it(looking down on the gun holding it as you would shoot it.)
One of these parts will connect to the trigger. It looks like this. http://glockmeister.com/product_info...roducts_id=287
You can see where it touches and interacts with the connector, which is the little part that is barely taller than the rail on that side of the gun.
That's where you put a drop.
ETA: People have varying opinions on James Yeager, but this video demonstrates exactly where you need to hit a Glock with lube. http://www.youtube.com/watch?v=pGobEpUO3Uc