A very easy achievement. I advise that you beat chapter one first and begin chapter two, so that you can use mission select and choose it without having to start over and reset the difficulty. That is of course if you are playing on anything other than easy (as it saves your main non-select playthrough.)
Anyway, select mission 1, set the difficulty to easy, and place the aim assist on high. Now as you play, make ample use of bullet time and the shoot-dodge especially (as the SD always seems to lock onto head.) Follow this and you should take little to no damage; I did not take any.