i used researching, farming and parenting. parenting skills is the easiest and fastest to accumulate for male villagers if you have a female villager over 50 years old. don't let them go the love shack anymore, just pick up and drop your villager over and over again beside your 50-year-old-female, but make sure that the "going indoors" shows as the action and refreshes everytime you pickup-and-drop your villager. and the bottom should also show "this villager improves in parenting".