Minecraft wiki entry for Curing_a_zombie_villager, associated text: Don't heal the zombie villager near any mob that attacks villagers, such as zombies and illagers. These mobs might not attack the zombie villager, but when the zombie villager is cured, they attack the newly-cured villager. For example, don't heal a zombie villager during a raid.
Moving your iron golems temporarily away from the village can be good since the iron golems attack zombie villagers, even while a zombie villager is getting cured, and the zombie villager always attacks iron golems. Once the zombie villager is cured, bring the iron golems back as your village may get wiped out by zombies if they don't patrol the paths.
Make your tamed wolves sit because they also attack the zombie villager until it dies if the zombie villager accidently attacks you.
If you're planning to shoot a weakness tipped arrow at a zombie villager to give it the weakness effect, don't use a bow enchanted with Power or Flame because it might kill the zombie villager in one hit or burn the zombie villager to death if you use the bow on it.
Punching the zombie villager with a weakness arrow doesn't give it the weakness effect.
Use a shield for safer blocking from zombie villager attacks since you don't want to harm the zombie villager when curing.
Don't let your zombie villager infect any more villagers when curing.
Moving a zombie villager into a village house with no beds is the best trapping place, because there is a door and you can build a wall in the tiny area of the house and the zombie villager cannot attack you, rather than outside, where you need to build four walls to prevent the zombie villager from attacking you. Make sure you close the door after trapping the zombie villager!
You can also let the zombie villager chase you after you fed the golden apple if you don't want to trap the zombie villager or get attacked by the zombie villager. Keep the zombie villager away from zombies while chasing.
If the witch throws the weakness splash potion on the zombie villager, the zombie villager attacks the witch. Don't worry about the witch killing the zombie villager with negative splash potions, as poison does nothing to the zombie villager, harming heals them, and slowness doesn't affect them as much because the witch barely moves when throwing or drinking a potion. Since the zombie villager already has the weakness effect, the witch doesn't throw another weakness potion at the zombie villager.
If you play on a realm or server and cure a villager, the discounted trades apply only to you. Everyone on the multiplayer world must cure the same villager themselves to get the discounted trades.