To begin, join any game of your choosing, ranked or unranked, and select your favorite map. For the sake of getting the achievement, I would suggest Dustbowl, as there is a constant area of combat where the people you will be healing take constant damage. By far, the best way to get the achievement is to find a Heavy, and have a constant healing beam on him as he gets torn apart by the enemy. Soldiers also work, but Heavys are much better, and people who play as them put themselves into the line of fire, allowing you to jump in and build up healing points. When there are no Heavys around, heal all friendlies around you until you spot someone who looks as if they are charging the enemy. You will most likely get this achievement naturally while playing, so a lot of effort really isn't needed. If you were to really go for just this achievement, I would guess it would take about an hour and a half to obtain.