Optimize website issue

Hello,

Our website loading time is too low (12s) http://www.nhadep.net, so we are doing difference optimizes in order to make our site load faster and optimized pages lead to higher visitors.

But still there are errors notices according to http://www.statscrop.com/tools/how-to-seo/?url=nhadep.net (as mentioned below), could you please advice us how to fix them?

Thanks.

e.g.
1. This site has more than 2 CSS HTTP request(s). The page could eliminate more than 1 HTTP request(s) if you combined all style sheets on the same host into one.

2. We did not find CSS-based print-friendly versions on your site. You can use the very same HTML but applying a different stylesheet, in which you can disable menus and other elements that make no sense on paper. Just use the media="print" attribute in your head link.

3. We found deeply-nested HTML tables on your site. If the site using deeply-nested HTML tables will be difficult to quickly display the page content.