From Mark Bittman's "How to Cook Everything" I usually don't thicken the filling for a simple apple pie, but if you want to make sure the juices don't run, add 1 1/2 Tablespoons cornstarch or instant tapioca when you toss the apples with the spices. I also keep spices to a minimum, since I'd rather taste the apple; you could safely double their quantity if you like a spicy pie, and add a pinch of all spice and/or cloves if you like.