What it is
The purpose of hitting is to swing to hit the ball. Try to make hard contact. When you swing with purpose, you get the barrel to the ball with the back hand. That is the main purpose.
Why it matters
A very important piece of the hitting puzzle is that the ball will tell you exactly what you are doing. Ball flight, direction, contact result and the miss itself all carry information. A swing with a purpose gives the ball something to tell you.
What to look for
Watch what the ball does: it tells you exactly what you are doing. Track the ball from the pitcher's hand into the hitting zone, then look at what the barrel did with it.
How to do it
Go to the plate to hit the ball hard, not just to put the bat on it. Track the ball from the pitcher's hand into the attack zone and let the back hand get the barrel to the ball. Then use what happened: learn the action, adjust it, and compete with it in the game. It does not matter what you do in BP if you cannot do it in the game.
What good looks like
Hard contact. The ball coming off the bat tells you whether the swing did its job, and the next at-bat shows whether the adjustment holds up in the game.