Your tagline should be the most succinct possible explanation of your essence. Make it specific. Make it accurate. Make it true. Does your paper towel soak up liquids faster than all the others? "Bounty. The quicker picker-upper." Do you have a specialty? "Kesslers. We do diamonds better than anyone, because diamonds are all we do." Don't be global and general. Be narrow and specific. "Jo to Go. fabulouscoffeefast." If your tagline doesn't differentiate you from your competitors in a meaningful way, kick it to the curb. If it doesn't raise the eyebrows of your friends, it isn't worth promoting to the public. Good taglines are the natural by-product of a focused business model. That's where you must begin. And may the Force be with you :)
With over 100 billion emails sent every day, it's getting harder and harder to stand out from the other scores of attention-seeking messages your customer deals with each day. But it's far from hopeless.