Part of what makes Settlers of Catan both balanced and exciting are two sets of slow-the-leader rules: The robber and trade embargoes. While this means you have a chance to win even after a slow start or a seemingly poor starting position, it conversely means it can be difficult to close out the game for victory after having a great starting position, making many great tactical decisions, and having the lead for most of the game. The most extreme example I've seen is the leading player with 8 victory points lose to a player who had 4 victory points, 10 to 9, as everyone successfully and almost completely stalled out the leader for many turns. Much more common are games where someone reaches 8 or 9 points first goes on to lose to someone with 2 fewer victory points.
Is there one (or a small set of) end play technique(s) that significantly increase(s) one's chances of winning when faced with opponents who competently employ slow-the-leader techniques?