You can get this trophy on the way to getting the Combo King Trophy. Follow the instructions bellow until you have at least 6 kills in a row to get this Trophy.
You definitely want to get the Zack Mask from getting an A range score on chapter 13 because this will increase the amount of time you have between kills to continue the combo.
Chapter 5 Full House is generally the best option (though the "Assault" chapter is pretty good as well). Right at the beginning, you'll see a man in the second room with a crowbar. Grab the crowbar, kill him and then kill the man in the adjoining room. From here, go back to where you picked up the crowbar, head through the south door into the hallway. Go down to the end of the hallway and turn into the bathroom on the left side where there are two men. Kill them quickly and sprint across the hall to the billiards room. Kill the Dog and the man in there quickly before heading back out into the hall.
Sprint along the hall headed right and kill the man and Dog headed towards you. Take the first right (this hallway goes down) and turn the corner. Throw your crowbar at the man in the kitchen to knock him down. Kill him with the crowbar. For the last part, you can take either the crowbar or the gun that this last man dropped but I recommend the gun. Go up and you'll see one last room filled with four men. Step through the door and then back into the hallway and just a little ways around the corner so they can't see you through the door. This should cause them to chase after you. Shoot through the door as they come or when they bottleneck near the door, run up and club them with the crowbar to dispatch them. Once you've done this and the level is clear, you'll get credit for a 13 kill combo and this trophy will unlock.
This is also good practice for getting high scores on other levels. A high combo multiplier is possibly the best way of getting high scores and the [Get A Life] Trophy.