The order and placement of things speak to your audience. Send a clear message!
In his recently completed product-a-day challenge, one of my favourite graphic design professionals, Dave Seah, created an excellent quick reference chart that shows you how the visual design hierarchy actually works. The design principles described apply to all products and communications you might create for your business, they are not limited to forms. When the elements of visual hierarchy are used correctly, they help you communicate content and marketing messages more effectively.
Dave has generously made a free download available to all: Visual Hierarchy Basics – US Letter [PDF].