Server Response Time
Full Page Caching can accelerate Magento site up to 200 ms for time to first byte. Use Crawler to be sure that no one visitor will not have uncached content.
Reduce static content size
You can reduce image size via auto-scaling and optimization. JS & CSS content also can be minified by removing excess content. Enabling GZIP compression will be good idea for optimization of content transport.
Decrease requests count
Merge several JS/CSS files to single. It will decrease requests count and will help bypass browser limit in simultaneous requests. Insert small js & css files to HTML page directly. Don't forget about usage browser cache.
Defer loading of JS, additional CSS and images. Be sure that user can see page as fast as it possible. Moving JS/CSS to the bottom of html page will help you in this. Lazy load of images will help to loading of images after end of page rendering.