It should be generally assumed that designs should be as simple as possible. So if you’re working directly with a competent designer, you need not say so. If your designer does not hold this as a core working principle, get a new one.
Client: “We’d like you to design a next-generation car dashboard for our new line of luxury vehicles. The car will feature all the latest gizmos: GPS, iPod integration, satellite radio, automatic environmental controls, you name it. And the interface needs to be simple. Google simple.”
Me: “Ok.. here’s what we’ll do. We’ll remove the wheel, pedals, and all conventional buttons and displays. Instead, we’ll mount an LCD to the dash, and display a single text input box. Voice recognition will fill in this box for the driver, and when (s)he says “Search”, the car computer will return the first 5 million commands (s)he most likely meant. The driver can then touch the command which they meant and have it execute. Alternatively, the driver can say “I’m feeling lucky!” to have the car automatically execute the most likely desired command, such as “Turn right”, or “OMG STOP NOW BEFORE WE DRIVE OFF THAT CLIFF!!!” If the driver survives long enough, they’ll get to enjoy the lumbar support and tunes from their iPod.”
Me: “We can call it ‘Sue-gle’.”