target that audience. Younger audiences appreciate form over substance while older more mature audiences appreciate substance over form.
Cover is key
Take time to pick the right photo for the cover and really think about the elements you are going to place on the cover. Again, think about your target audience.
don't be afraid to use every bell and whistle the design software has to offer, but just have a purpose. Even if the purpose is that you like the way it looks. Dont just do it because you can.