This is simple achievement but this guide will help for all 50 waves across all of the maps. All of the maps are constructed in a square shape, which will allow for you to place a turret at the centre of one of the ends of the map, and allow you also to see all the enemies coming towards you, giving you the chance to pick them all off, end the round and pick up all of their points before the next round starts. This method also helps a lot when it comes to the boss waves.