Before the day
A clear tagline that names the problem, a gallery with real screenshots or a short video, a maker comment that tells the story and what feedback you want, and a working signup with a trial or free tier.
On the day
Launch at the start of the Product Hunt day (Pacific time). Tell your own audience once, honestly. Never buy votes or ask for upvotes in groups: it can get the launch removed. Answer every comment the same day.
What to expect
A launch that isn't featured usually brings 100-500 visitors. A Show HN post has a median of about 2 points. Both are worth doing, and neither replaces steady work in communities and search.
After the day
Thank people who commented, follow up with anyone who signed up, and measure which source sent the visitors who stayed. In GTMorganic, a launch is a step in your plan with its own tracking link, so its visits show up as Tracked.