Reorder Js and CSS file in header

I am looking for some way reorder the Js and css files in header section.
How to make sure that js comes in one block and css comes in one block.
when I install a plugin/widget then new css or js files get added.

My concern is page speed. Google page-speed suggest an order for js and css file. All css files should come first and then all external js. Better put all js at bottom if that is not modifying any content at load time.

But how to ensure it. It there a way from where I can start!