The setting document title document kind of works for title's only, but you'd need full control over your whole head section.
There is a good article that walks you through how to implement the third party ms-seo package which is basically a javascript set of tools to properly manage the contents of your document's head section.
Having done this, it is the spiderable package's (built in meteor core package) job to expose your pages to search engines.
When your web site is a big javascript app and your body section is virtually empty, you need to tell the search engine that you are a web app, not a regular web site. When the search engine is informed that you are not a regular web site, it uses specially crafted url's to access your site. As a developer, your job would be to detect the calls to these special url's to present a static version of your site.
Meteor's spiderable package automates this task for you. In the background, it uses a javascript package called PhantomJS that is a server side full stack browser that sees your site just as a normal user would and provides the output to the search engine. And woila!, you get yourself SEO :)