You will most likely stumble upon this achievement just by playing but if you're having trouble getting this achievement the easiest way around this would be to play as a slayer, find a mob of enemies and get them as close together as possible then do the standard attack followed by upward slash (B button) and then repeat the combo or add a mix of your own skills in here and there and you should get it by the end of the second loop if not the start of your third combo loop.
If you vote negative please leave a comment why and ill be happy to fix it.