Ask HN: Best ways to market an app for free?

Built an app called Rudder that enables users to receive quick feedback on upcoming decisions. It’s Survey Monkey, but geared towards being social and fun. We think the target audience is 18-30 year olds, skewing female. My core marketing initiatives have been: outreach to tech sites and bloggers, and social media campaigns. But other than that, I'm not sure how to get my product out there.