As basic to optimize a new website. You need to concern on the onsite SEO so you do not need to get back to your site and make changes all over again in order to help in SEO .
Submit sitemap ,
Optimize your meta tags with strong keywords use in meta title and meta descriptions,
Use H1 title tax ,
Set ALT and Title Tag on every image of your sites,
SEO is important steps in new website in order to get traffic and compete with others.