Just like the description says: Heal other Survivors for 10 health states while at least 3 Survivors are injured, dying or hooked.
The achievement tracks every percent healed. If a survivor is down and recovered to 95%, when you heal him up to injured state, you will get 5% towards 1 healing of other survivors for the achievement. You do not get the full 10% towards the achievement just because you changed a survivor state by healing. On the upside this also means that if you heal a downed survivor for 20% and the killer chases you away, you will still get credit for that 20% towards 1 full heal.
While the objective is simple, the execution may be a little bit more challenging. A lot of people tend to heal themselves whenever the chance presents itself, so it can be tricky sometimes to have 3 people injured or incapacitated at the same time. In general this is easier in the high aka red ranks as people tend to power through gens when injured.
The only injured survivor you can control is yourself. While you can run the perk “No Mither”, so you are always in the injured state, you probably will become the focus of the killer. So personally I would advise against running that perk and just take a protection or distraction hit. When the killer downs someone, quickly draw his attention and take a hit and run off. Or when the killer carries someone to the hook, take the hit and run. The killer will probably apply gen pressure after the hook and chase a third survivor. When he takes a hit, unhook the first survivor and heal him.
You can bring a medkit for quicker healing.
* Botany Knowledge - Healing speed and efficiency of healing items is increased.
* We’ll Make It - For each Survivor you rescue from a Hook, gain an additional 100 % speed increase to healing up others for 30/60/90 seconds.
* Autodidact - For every successful Skill Check completed while healing a Survivor, you receive a Token for a maximum of 3/4/5 Tokens. Each Token grants you a +15 % bonus progression for a successful Skill Check while healing Survivors.
I suggest running We’ll Make it and Botany Knowledge. There are other perks that increase action speed in general but their effect is negligible.