Alright lets start by creaming (mixing well) the cup of butter and shortening together in your big mixing bowl with that electric mixer.
If you don't have an electic mixer then do it with a whisk and a fork and a lot of elbow grease. It gets harder to mix when you add all that flour in. I give you my sympathy because I've had to do it before.
If you have a big fancy Cuisinart that can do all the work for you then I forgot to tell you that you're supposed to do it with just a fork and you get no sympathy. >:P