You can develop your message with key points (we solve customer problems fast by being available 24/7, by hiring the best reps . . . by talking really, really quickly), but key points are not the main message.
Let's assume your audience is thinking about a thousand things—for example, food (what to eat; when to eat; with whom & where; what's already been eaten; what else could be eaten; how much food is reasonable for one person to actually consume in a day; is it a mistake to skip breakfast?)—and will immediately forget almost everything you say.
What's the one thing you want them to remember?
That's your main message. And while there's no reason for your main message to be a snappy ad slogan, still, we can learn a lot from snappy ad slogans.
1) Use plain English.
"When it absolutely, positively has to be there overnight," promised FedEx.
The "absolutely, positively" part sounds like a real human being, worried about a real package.
FedEx could have used those 10 words from before ("Relax. We're dedicated to customer-centric, results-driven, streamlined solutions").
But that would have caused widespread panic.
2) Focus on one thing.
Compare these two slogans from Wal-Mart:
a) "Always the low price. Always."
b) "Save $. Live better."
I like the first. A main message is one thing, not two or three. And I really like the repetitive "always."
For the same reason, "Sheer driving pleasure" (BMW) beats "Power, Beauty and Soul" (Aston Martin). Power, beauty and soul add up to three abstractions—that's a laundry list, not a car.
3) Be concise.
The best slogans from the past 100 years are under 10 words. Consider:
Avis: "We try harder."
Wendy's: "Where's the beef?"
Apple: "Think different." And before Apple, the motto at IBM was simply, "Think."
A short message is like Lite Beer from Miller: "Everything you always wanted . . . And less."
Tip: Know your main message. Then, make sure your audience does too.