The short answer: Where everyone will see it.
The long answer: In a highly visible place where the family either congregates or regularly passes. I have mine in my kitchen right by my pantry and back door. We walk by it at least 15 times a day. I can see it from the sink, the dishwasher, the fridge and my desk area. I regularly glance at it to remind me what we have coming up that week and how far away our next trip or vacation is (usually it's not soon enough :)).
Crystal, an interior designer, formatted the calendar so that you could hang it in a high traffic area without it taking up a lot of visual space or detracting from your decor. The clean simple lines of the calendar coupled with our teak frame allows the calendar to blend with whatever design elements you have going.
Looking at the calendar regularly helps you stay organized. Hanging the calendar in a high traffic area makes it even easier to stay organized and spend more time living your life and less time trying to organize it.