By this stage, you should have a Joomla website that has been optimized perfectly as far as on-site SEO factors is concerned. Even without doing anything further, your site might start ranking pretty high, dependant on the search terms you are aiming for.
However, if there is a lot of SEO competition going on, this might only be half the work you need to do. Especially link-building is crucial if you want your site to be between the top-competitors.
This is not a Joomla related topic however, so I advise you to go on the web, read about the subject, and promote your site. Just some quick tips that are not expensive and work well to get you started:
- Use Google sites and tools to mention your site. It's Google you want to please, so use it: Youtube, Picasa, News, Places, etc. Just link to your site in the comment-section.
- Use your own social media to at least mention your site: Twitter, Facebook, Pinterest
- Paying to get your site indexed by search enguines is something you should never do. The good ones will find you anyhow. If you do want to speed this up, use a free service like Entireweb.
- Addme.com is also a site that submits your site to some directories for free. Only do these last 2 if you don't mind getting included in their mailinglists.
But don't forget to actually promote your site and spend time doing so. Great results take effort. Keep creating interesting articles on a blog-section of your site that people will love to link to. ALso Google loves sites that keep spitting out great content.