@HDN Rick mentioned it early on. The first key is mastering the duck and jump maneuvers. Besides that, I try to eliminate as many agents as I can when riding on elevators. Killing agents is your biggest source of scoring points. Their point value increases from 100 to 150 from floor 20 or whatever floor it is once you get past the initial floors where all the floors are lit up. So, what I’m trying to say is I’m not rushing to get to the car in the garage. I try to score at least 8k-10k on each level. If I sped through the first level, I’d only score 5k-6k when I reach the car.
The only other pointer I can think of is this. I do most of my kills while riding the elevator. I get the enemy to take a shot so I can shoot them safely without evading return fire while they reload. I do this by while coming down on the elevator, I pull back up the elevator when the bottom of the elevator reaches the chest of the enemy. He will draw his gun and shoot. I then go back down and kill him in safety. In the early levels, they reload slowly. Killing enemies on higher floors while riding up in the elevator is easier as I can kill them without exposing myself to their bullets and don’t need to get them to shoot first. I shoot right when the my gun clears the bottom of the floor and then move the elevator back down. I can try to video record this if it isn’t clear.
One other tip is to avoid engaging in a shoot out while on a wide floor (where the elevator is on the left or right edge of the floor). You can easily get surrounded to the right and left. Also, when there are multiple enemies to one side of you, sometimes one will shoot high and the other shoots low and you can’t dodge both. This is why I like to shoot and kill while riding an elevator.