I'm tackling this problem at my startup, ParkGrades.com, by: 1. Seeding the site with as much quality information as I possibly can (given my limited resources)

I'm tackling this problem at my startup, ParkGrades.com, by: 1. Seeding the site with as much quality information as I possibly can (given my limited resources); 2. Incenting users to add content through giveaways; 3. Testing the giveaways to see which incentives work best. Once a given area/topic has a certain amount of information, it's then much easier to promote that area/topic with additional marketing and incentives.