Healer and master gatherer is the most difficult skill to learn. You can train your healer set your villager preferences to healer and don't pick poisonous frog on your village so you will get many sick villagers to increase healers skill. You need 2 healer so if one healer get sick you still got one healer who can perform cure. Every a few days you will get trivia to help someone on a boat,just help her to shore and you will get master healer. Train master healer to gather things until she master it. After your master healer master three other skill you will get chief.