<link rel="dns-prefetch" href="//example.com">  //prefetch dns of domain which will be soon needed.
<link rel="prefetch" href="//example.com/demo.html"> //prefecth whole page or assets which the user woould most probably move next.
<link rel="preload" href="//example.com/demo.html"> //preload whole page or assets which will be required in same page