I just launched my iOS app this month.
https://itunes.apple.com/ca/app/just-add-pepper/id1225081155?mt=8
To spread the word I made posts on reddit, hackernews and Product Hunt. Your mileage may vary but from my experience posting on reddit resulted in a small bump in downloads. You can see the blips on June 13th and on June 20th.
I posted in some targetted subreddits like /r/cooking and also some general ones like /r/apple and /r/iPad. My post on hackernews got no traction. I saw a significant bump in downloads after posting on Product Hunt. The spikes on June 28th and June 29th are a result of that post. It got about 100 likes on the day it was posted and was ranked around ~10th place.
What other strategies have you guy's used to promote your website/app/startup?
I just wanted to say that with HN you have to insist. I had sent my app (https://everydaycheck.com) about 5 times without luck and then gave up. But 3 days ago, I saw the top Show HN post was "Hackerhunt", a web that gave a lot of visibility to Show HN. So I immediately posted my app again and got lucky. I guess I can say I rode the wave :P
Great point. Luck is a factor in how successful your post is. I would also consider day of the week, Wednesday or earlier in the week seems to result in better traction. Also time of day is important. I usually post at noon, early in the morning or in the evening when people are off work hours.