Focus on running faster, not harder.
I would normally come off the turn with 300 to go and launch into a full sprint, in a normal even paced race. Obviously championship races are different. But, if I ran my race, I always had a really good last 300-400 left in me. I'm not sure how, as I usually thought, as I approached the bell, "there's no way I can do it this time, I'm exhausted." But I always did.
I used a few shorter steps as I was finishing the turn and entering the back stretch to get my legs moving faster, then I opened up my stride and launched into a full sprint as I hit the straight away.