Most pies are best eaten fresh. But if you have to freeze a pie, the best way is to assemble a double-crust fruit pie ahead of time and store it in the freezer unbaked. These pies freeze well and can go straight from the freezer to the oven. Don't try the same thing with custard or cream pies because the freezing and thawing can cause the fillings to separate or weep.
It's also a good idea to prepare your pie shell ahead of time and freeze it unbaked. It will keep this way for several months.