1.[First 5 Steps] All out. You need to set the tone in the beginning. Attacking the first 5 steps aggressively will put you in great position for the first 50m. 

2.[0-50m] Get out quick. Reach top speed. This is going to be the fastest part of the race. It is easier to gain speed in the first 100 than the last 100. 

3.[50-200] FLOAT. Palms facing in. At this point, you are not accelerating anymore. You are taking your foot off the pedal(Riding off the speed you produced from the first 50m). Do what you can to "decelerate slowly."

4.[200-310] Reaccelerate. Treat this 110 like you are running up hill.

5.[310-400]Step over, drive down. Exaggerated arm swing. This has to be accomplished because you will be losing a lot of momentum in this part of the race.

*Every successful 400m runner has a race plan. To enter a race without one; you are spelling complete disaster. Having a race plan will ensure that you distribute you energies properly throughout the whole race.