To get this achievement, you have to be the highest scoring player in a multiplayer match. Using a sniper rifle allows you to quickly take out a spotted target without having to approach them and risk getting hit. Staying with your team in team matches and staying away from open areas also helps reduce your risk of death. Shotguns work well at close range. Weapons with a high rate of fire like assault rifles work at close and long range, and also on groups of enemies. Combo kills, in which multiple enemies are killed in rapid succession boost your score.