In order to come in first place, you have to kill the most robots. This can be done simply by starting up the survival level on Chapter 1 with 4 players. The 3 players NOT going for the achievement should die as soon as possible without shooting any robots. Let the remaining player finish the first wave and die when the bonus wave starts. You must beat the first wave or else it will not count as you beating the level and you won't get the achievement.
You can find players to help you with this HERE.