I'm building a ride sharing app, that finds you a ride with acquaintances or someone you have at least a mutual friend with.
That said, I would love to know more about mistakes and successes you had when you launched your first app
I cannot stress enough the importance of reviewing the App Store Review Guidelines before submitting your app. My recent app got rejected because of a problem that I literally fixed in 5 seconds, but I have to wait another week before it will be reviewed again. Don't let that happen to you.
https://developer.apple.com/appstore/resources/approval/guid...
Marketing
Think about how you will market your app. For your app, I would research the marketing origins of startups like Uber and Lyft. A "Show HN" is a great place to get feedback, but it is unlikely that the HN community is your target market. Go to Twitter, Google+ Communities, and find forums tailored to carpooling and ride sharing. Hit the blogs!Often times, moderators of blogs will give you FREE advertisement, just because you made something that their readers will enjoy. Do not spam, and hang around in each community you post in for a while. Then, if you haven't already, start a blog. Start writing about your app, carpooling, and other things that you want to be known for.
Here are some well-known blogs that are great for learning how to market your products:
http://brennandunn.com/ - This one is focused more on freelancers, but Brennan provides really helpful advice that applies to almost all situations