no1 is from the LCD and plugs in top right of logic board just below the camera (it lies horizontally)
no2 is from the digitiser and sits to the left of no1 and a little lower ( it lies vertically)
both these connections snap on to the corresponding connector
no3 from earpiece/proximity sensor slides in- tab slides from the top of the logic board, into/under the white connector and then you close the black (or in some cases white) lid over. this tab doesn't need to be pushed in all the way to the white line, once it feels snug stop pushing. this connector is immediately above connector 2.
the correct order for replacing the connectors so the lid closes is 3, 2, 1. the connectors all end up with the cable needed directly over them as you prepare to close up... so there shouldn't be too much confusion. chose any guide for this phone and you should see the numbered cables on there! iPhone 3G Front Panel Replacement