Build relationships with journalists
PR is a long term game. To play it well, you need to develop relationships with journalists over time. Engage with them on Twitter, find ways to add value, meet them at conferences, etc.
Create a list of journalists you will pitch to
Go to publications that your target audience reads and find the journalists within those publications who tend to cover the kind of thing that you are pitching. Pitching a specific journalist will generally give you a better success rate than a generic pitch. Volume matters because whether someone will cover your story can be very circumstantial (they may have 3 other important stories that week
Create a press kit
A press kit is usually shared folder that contains some basic things that make it easier to cover your product. These can include logos, screenshots and GIFs of your product, images of founders or other pictures that could add interest to the article, and sometimes a press release.
Send email pitches to each journalist
A week or two before launch, send your email pitches. The content of this pitch is really important. It should communicate the problem your product is trying to solve, what your product does, and why it is unique and newsworthy (which could include tying it to some bigger trend or adding in a unique part of your story).
Make sure to include the basics too: when your product launches (and if you want them to wait to publish until a specific day/time), how much it costs, the landing page URL, the press kit URL, and any information they need to access the product for free.
Follow up
Journalists are busy. Don’t be pesky but do follow up if you haven’t heard back (and definitely follow up if they respond back to you).