You want to avoid reaching or straining your neck and shoulders. But if you can't prevent harsh overhead lighting, glare filters can help. Your work surface dictates how everything else will be set up. If you insist on using an old desk, consider modifying it to fit you better. To get the proper leg clearance, for instance, you might have to take out the center drawer.
Dry eyes cause redness and strain.
Reduce eye strain by periodically looking away. Every 15 minutes or so, focus on an object at lest 20 feet away. Imagine a huge box around you. Rotate your eyes to each corner of the box at least three times in one direction, then reverse the direction. Rub your hands together as if to warm them, then place the cup of your hands over your closed eyes.