If you have, or can get a copy of the newer, Gen. 3, Glock owners manual on page 37 (figure 14) it has a photo of where to put one drop of oil between the trigger bar and the connector. With the slide off, at the right rear of the frame (lower part of the pistol) looking from above you will see a very small silver tab that is curved sticking up. That is the top of the connector. The trigger bar runs along the right side of the frame and slides along the connector. If you don't want to, or don't know how to remove the lower trigger assembly (not necessary), just put one drop of oil between the tab and the trigger bar. It will flow down to where its needed.
Some people don't do it, but the Glock manual states: "Most importantly, a drop of oil is needed (Figure 14) where the rear end of the trigger bar touches the connector at the right rear corner of the frame."