Comfort, confidence, and balance! You need all three of these characteristics when you step into the box to hit.
Confidence begins when you step into the box. Do it with a sense of purpose; dig your back foot in and let the opposing pitcher that you're there to battle.
Comfort and balance depend on your stance and how you prepare to hit the ball. If you're not comfortable, you won't be relaxed. When working on your stance, strive for a position that comfortably puts you in a balanced position to hit.
The first priority when getting into your stance is to make sure you have good plate coverage. Have a method for determining this for each at bat. During practice, have someone watch you take some practice swings from in front of the mound. Simulate swinging at an outside pitch. Is your bat covering the outside corner? Adjust your distance to the plate so you have the correct distance.
Create a method for measuring that distance. Many players tap the plate with their bat the same way each time they get into the box. If the bat hits the same part of the plate each time, then they know the distance is correct.
While every player wants good plate coverage, the depth you stand in the box is more a matter of preference. If you stand deep in the box (towards the catcher), you may have more time to wait on a fastball, but you may find it more difficult to hit breaking pitches. By standing forward in the box, you may be able to catch the breaking pitch early but it will be more difficult to get around on a good fastball.
What's the right position for you? Analyze your strengths and weaknesses to help you decide. But, wherever you stand make sure you feel confident in that position. Most big league hitters tend to stand toward the back of the box. You, like most of them, may find the extra time to react is important.
Most hitting coaches claim that the best stance for hitting is a square stance -- where your feet are parallel to the plate. This stance puts your body in the best position to coil, stride, and swing.
However, there are other stances and you have decide what works best for you. Try to avoid radical stances at the plate, experiment with stances that give you the ability to make a smooth coil (discussed later) to get into the launching position.
When you get into your stance, your weight should be slightly back, but not completely on the back leg. Have your hands near the top of the strike zone. Many players prefer to have their hands slightly off the back shoulder. Having your hands off your shoulder and at the top of the strike zone puts them in the best position for swinging the bat. It's very difficult for any hitter to catch up to a high fastball and hit anything but a pop fly if their hands start below the ball.