Most launch advice starts with the day itself, which is the wrong end of the problem. By the time you post, the result has already been settled by how many people were paying attention the week before.
Start where people are already looking
Directories are the cheapest way to be found by someone already searching for what you built. Product Hunt still moves the most traffic in a day, but the listings that keep working are the narrow ones — the directory your buyer checks when they have a problem, not the one the industry checks for news.
Communities are slower and worth more. A founder who has been useful in a forum since March gets a different reception in June than one who turns up holding a link.
Then time the public push for a moment worth clicking. A launch is not an announcement — it is the day the thing you built quietly becomes easy for a stranger to try.