You have to "baby-sit" a lot of newbies to keep them on task at first. After they reach Trainee they should continue at that skill on their own. However, with some I've had, I've had to constantly catch them and put them back on task all the way until the reached Adept. That can be a pain.

Check their likes and dislikes. Villagers who like to relax, dance, play, etc. or dislike work, lifting, etc. are much harder to keep on task... and forget about teaching Farming to a villager who dislikes fish. lol Not going to happen if the ocean can be fished.