I think "promote" is part of the equation itself. What makes a city good for tourists isn't usually what makes it good for residents. What makes it good for relocating businesses has a complicated relationship to the benefit of residents.

That said, what makes a city livable to me - in fact, the whole point of living in a city or town rather than in the country - are the cultural opportunities. What's the music scene like (both classical and popular)? How many art shows and galleries? Is there a year-round farmer's market (and is it required to offer only locally produced goods)? Are there good ethnic restaurants, and other opportunities to be exposed to non-dominant cultures? Is there a diverse racial make-up to the population? Is public transit efficient and clean? What about pro sports?

If I had to choose one thing to improve in each of my towns, it would definitely be public transit. I'd know whom to contact, but I'd also know that it was futile, since it's a matter of constant debate. Outside of the major cities (and not even all of those), most American jurisdictions invest very grudgingly in infrastructure, public transit in particular.