This achievement is pretty self-explanatory. Just make sure to use ranged weapons as often as possible. It definitely helps to upgrade your ranged weapon damage on the Road to Rule, because that will just let you dispatch your enemies more quickly. It's just personal choice really between pistols/rifles/etc. so just pick a weapon that suits your play style. Some people like firearms that shoot quickly, where others will find this achievement easier to come by with slower firearms that do more damage.