The cleaning process of projector screens has been discussed in-depth but this question actually refers to a much larger point. Anytime you see dust or grime on your screen, it is wise to clean it as this can improve the picture quality and integrity of the screen. However, when the time comes to store it away for the winter, you need to pay a little more close to attention. For one, you need to ensure that no debris (such as leaves) has been lodged in the screen. If you notice anything like this, remove it before storing the screen.
But, you should also perform one last through clean for the year. To do so, once again, abide by the manufacturer’s recommendations. One last thing, assess your projector screen for any damage and get it fixed beforehand as there is nothing worse than realizing you have not fixed it yet for the new year.