First step might be to have some strangers look over the site to give feedback and catch any details you might have missed when looking at the site every day during development
You don't want to start sending traffic to a site that isn't ready to engage visitors properly.
Without knowing some general details about the site (printing services, clothing line, manufacturer), it's hard to give specific details about your "first step".
One thing you can do in any niche is: figure out who your customers are and find the most appropriate ways to get your products in front of them.
That could mean you advertise on a blog, in a newsletter, submit a press release, etc.
What do you already have in your marketing plan for your business? That way we can suggest things that you haven't already thought of.