Drupal is module based CMS, so you are going to need only a couple of modules added to your installation. Each module and its use follows. Hopefully this article will be updated quite a few times.
PHP filter + Browscap
There are a couple of Drupal modules that allow hiding content based on device size (mobile or desktop). Tried quite a few Mobility modules, but none of them seem to work, where old or required modules like Cache to be turned off. And its not what I wanted.
In mobile versions I sometimes disable large slideshow blocks or page images, if you are up for that, here is what you do: download browscap, deploy it and enable both modules (PHP filter is native Drupal module). Open you block, enable PHP condition and paste this snippet:
Full module name is Advanced CSS/JS Aggregation. This module combines (even cached) css files into a single file, which gives quite a few performance points in some of SEO evaluation tools. Combining your CSS files also reduces text/html ratio. Setup has quite a few tabs, but just follow the setup and enable CSS compression.
Usage of all these modules above may improve your website SEO evaluation by up to 10%. If not, then they will at least improve your page loading speed and overall performance compared to your competitors. Any feedback to this article is highly appreciated.