One of the mistakes many business owners do is that they start promoting their product after the launch. The better way is to plan the product launch campaign at least 3-6 months prior to the exact date of the launch.
If the website isn't ready before the launch, you can create a simple landing page displaying the date of the product launch and a signUp form to stay updated.
Also, you can submit press releases to get early traction for your business and product as well.