I don't know how other folks lay out their cards, but I start with the cover, and then for me, it determines the rest.
I don't lay out my colors or anything beforehand, because I don't really know what I am going to do...I like to let the designs of the papers guide me. It took a while to decide what to do to the inside, but I kinda like the idea of giving a little something extra and making things "useful"... so I added some cute tags ready for the recipient to play with.