It depends what your website is all about.
But start with the basics:
1. Make sure your onsite SEO is done correctly.
2. Submit it to search engines.
3. Submit your site to directories under the right category.
4. Build backlinks
5. Create a Facebook Page and Twitter account that is related to your site.
6. Post updates on your Facebook and Twitter regularly.
7. Post new content on your website regularly.
There's much more that you can do...