Dressed to Kill is an achievement in Blood and Wine expansion and requires one to equip all 6 pieces of grandmaster witcher gear from one of the Witcher schools.
The 6 pieces include:
- armor
- trousers
- gauntlets
- boots
- steel sword
- silver sword
To start, go speak with Lazare Lafargue and he'll give you the secondary quest Master Master Master Master! which then gives you access to the 5 grandmaster gear quests, though you only need to complete 1 for this achievement's purposes.
Once you have a set, have him craft all the pieces and equip them to get the achievement to unlock.