Define page size and layout in new score wizard
One of my (tiny) frustrations with MuseScore is that the default page size is A4, while (like most North American users) my printer vastly prefers 8.5x11. I'm also a person who, from time to time, likes my scores in landscape orientation.
My suggestion: Make some basic page layout options part of the new score setup wizard. (They should still be part of the Page Layout menu, of course.) Not only would this be convenient, but it will be extremely helpful for North American users who aren't aware that A4 is MuseScore's default page size.