If I could tell one thing to clients I've worked with over the past 23 years, it's this: Say one thing.
It's hard to stick to one message. Especially since articulating one message generally takes far less than 30 seconds. So clients think that if it takes five seconds to say that your snack food is make with no artificial ingredients, you still have 55 seconds left to add that it comes in seven fun flavors and four convenient sizes, is available in the snack aisle, has an exciting new label, is fun to eat, and is enjoyed by some celebrity who is utterly irrelevant to the message they want to communicate, but who they pay ridiculous amounts of money to in order to be photographed eating it.
The thing is, expressing what you want to communicate isn't the same thing as communicating it. Or to put it in a way that even some of my most bone-headed clients could actually understand, it takes less than four seconds to say, "Brian Belefant is incredibly good-looking." But I guarantee it'll take longer than 30 seconds to convince you that the statement is true.
Say one thing. And say it well. If once you've crafted your message you realize that you actually need less than 30 seconds to communicate it in the most compelling manner possible, don't screw it up by throwing more information at the viewers. Run shorter ads.