Annoying glare that results when sunlight shines directly on the screen can make it impossible to use the computer at various times of the day.
Minimize potential glare by placing the computer at right angles to the windows and by installing window blinds.
Blinds provide the greatest flexibility since they can be opened wide on dark days or closed tightly when the sun shines brightly. By adjusting the angle of the blinds, you can provide a little or a lot of screening.
If the glare is coming from an overhead fixture or a skylight, a hood available in computer supply outlets can minimize the problem. If nothing else works, be prepared to change a fixture or to not use the overhead light when the computer is on. You can purchase a task light to illuminate the writing surface of the desk.