How to fix PageSpeed Insights issues?

How to fix PageSpeed Insights issues?

<?php  if(!strpos($_SERVER['HTTP_USER_AGENT'],'Google Page Speed Insights')){?>
<jdoc:include type="head" />
<?php } ?>


So the code could go something like:

if (strpos($_SERVER['HTTP_USER_AGENT'],"Google Page Speed Insights") == FALSE) {
    //load our elements
}