Increase the amount of parallel downloads

This is something that can really make a difference, but this is an optimization field that is not very well known. Browser don't download all your files in parallel, they always only download one, two or maybe three files in parallel, this is why your browser Network Tab (firefox firebug / chrome developer tools) shows a so called waterfall of downloads. To fix this you have two options. The http 1.1 specification for example recommends no more then two parallel downloads.

You could try to put your static files, like images on different hostnames. Those can be different domains or sub-domains. You could put images on static1.example.com and other on static2.example.com or setup a cdn at cdn.some_cdn_host.com and put files there to increase the amount of parallel downloads.

Another solution to this problem is to use the new protocol from Google called SPDY. If you want to use Spdy, you will have to have an SSL certificate and serve pages using SSL. The big advantage of using SPDY, is that all the files of your webpage can be served simultaneously. SPDY does not work with every browser an can't be used on every server but (most of them) some do. Hopefully more servers and browser will support SPDY. First the clients that support SPDY today are: the newest versions of Firefox (11+) and Chrome (Chromium). So users using one of those two browser will benefit from SPDY. Second the servers that have SPDY modules are: Apache and Nginx, so around 70% of all servers. Apache 2.2 has a SPDY module and Nginx has a SPDY patch that is available for the 1.3 development branch.