Eyes with the barrel
The single biggest key to becoming a great hitter. Seeing the ball early and seeing it longer allow the hitter to swing at pitches that are meant to be hit hard and maximize force at the point of contact.
In practice, keep the thought, "eyes with the barrel." This keeps the eyes and the barrel of the bat on the ball longer and allows force to be delivered through the point of contact.
Balance = Strength
Many hitters lose force and consistency in their swing when they lose balance.
In practice, attack the ball aggressively but challenge yourself to hold your finish for a count of two.
If you can finish with balance, you were balanced at contact.
Balance at contact also means strength at contact and maximizes opportunities to hit the ball hard.