W = Watch the ball hit the bat (many/most young players turn their head w/ their swing).

I = In front of the plate (most young players try to make contact over the plate, and are almost always late).

N = Never chase garbage pitches (...w/ 2 strikes, sometimes you need to swing at a borderline bad pitch, but never garbage).

That's all they should think about in games. In practice you can go over things like snapping the bat through the ball w/ wrists, and getting the hands inside the ball, but you need to make it clear that they need to hit by only W.I.N. and habit in the games, or else they will be thinking too many things and will have extremely late swings during games.