Great slogans are one of the most powerful forms of brand property. This is especially true when the slogan is a big brand idea that works as a "rallying call" for people inside the business, in addition to creating awareness and meaning for consumers (e.g. "Keep Walking" for Johnnie Walker and "Live Well for Less" for Sainsbury's).
Laura Ries recently published a book called "Battle Cry" with some tips on creating slogans, building on work published by her dad Al, back in 2008, here. Al and Laura suggest five memory-building tactics, which seem to be surprisingly under-used. In Al's random survey of 266 slogans, only 19 used any one of these.
Rhyming can be a highly effective way of getting your slogan recalled, and has been used in some of the most famous campaigns in history. To name but a few: "A Mars a day helps you work, rest and play", "Beanz meanz Heinz" and "Milk's gotta a lotta bottle"
Using a series of words starting with the same letter can help a concept stick in the mind. This works for brands (e.g. Coca-Cola, Bed Bath & Beyond, Grey Goose, Magic Markers, Chris Craft, California Closets, Dirt Devil). Alliteration also helps a slogan "trip off the tongue", such as M&Ms: "Melts in your mouth -- not in your hand."
Play on words
This tactic is to use a play on words, such as the use of a double meaning. Al quotes as an example Saatchi & Saatchi's famous campaign for the Conservative Party in the 1979 U.K. general election: "Labour isn't working." This suggested that labour wasn't working, as millions were unemployed, and this in turn was because the opposing Labour Party was ineffective.
Repetition is about adding in extra words for emphasis, as Al explains: "Federal Express didn't get off the ground with the slogan 'When it has to be there overnight.' Rather, the ad agency Carl Ally added two words that made all the difference: 'When it absolutely, positively has to be there overnight."'
"Reversals are memorable as they vibrate between two meanings, forever embedding a concept in consumers' minds," says Al. An example of this is the line from Shakespeare's Hamlet, "To be or not to be: that is the question". An example of this would be the Holiday Inn slogan "The best surprise is no surprise".
So, if you're stuck trying to create a slogan, the tips above might help you. For more tips and tricks, there is a whole website called Adslogans here.