Before starting development, and especially during development, keep an eye on a very broad set of Google Alerts that blanket your market. Read each alert caref

Before starting development, and especially during development, keep an eye on a very broad set of Google Alerts that blanket your market. Read each alert carefully and identify websites that talk about your market or your competitors. This will give you a list of places you can start a conversation with. So while you're preparing for launch, keep notes of each candidate website. Notes to keep: name of the author of the article, URL of the article, when it was written, etc. Now when you can share something, email them saying you read their article about X and thought they might be interested in this new thing you just built. Tell them very briefly (2-3 sentences) what your new thing does/is and how it's different, and give them your contact details (including phone or Skype - some like to chat). This strategy becomes more important after launch as you don't have to wait before getting in touch. You can email them immediately as they can see your live product.