Routing is much of the answer. If they can get a better routing - but then EVERY crew is trying to get a better routing!
I recall a trip back from CDG in the late 80s. We were the last BA out of the day and had been delayed to about 23:00. The Captain did say that he would get us back before the curfew. Because everyone else had gone and the route to LHR was empty, the wheels-to-wheels time was 30 minutes! Smartly into T2 and away! Just remembered, it was a Tristar with that mechanical lifting L1 door.