Good question!!!
Couple items that might help
Be short/brief - You do not want to be to complicated. Make a list of things that make your business or would describe your business. This will help
Unique/Original - Do not make it similar to others as you do not want to remind anyone of someone else right?
Value the message - As it will be in your messages delivered (business cards, flyers, etc...) people will be associating it with your business.
Honesty - Make sure you show case the best thing you or business is going to bring to the table. Last thing you want is to break your statement. I.e. "We are never late" but you are late.... People will lose trust and it will hurt your reputation.
Emphasize on key items - Think of the company values, make a list this will help.