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. 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. 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. Analyze your strengths and weaknesses to help you decide. But, wherever you stand make sure you feel confident in that position.