I use Lucas grease and Lucas oil. If the trigger starts to feel crunchy, I clean off the old lube from the connector and trigger bar and re-apply. I put grease where the connector meets the trigger bar, and a little more on the outboard side of the trigger bar where it rubs against the frame. (Bright spots usually tell me where to put grease.)

A tip I got (not sure if it was from here or some other online source) was to put a bit of oil or grease in the stirrup that links the trigger bar to the trigger return spring. It's helped a bit.