To make your website loading faster and improve your pagespeed score, you have to enable Gzip compression and to allow browser caching for all static assets. For Plesk Onyx, you can add the following settings in the Additional nginx directives of your website or directly in your service plan settings.
# Enable Gzip compression
gzip on;
gzip_disable "msie6";
gzip_vary on;
gzip_proxied any;
gzip_comp_level 6;
gzip_buffers 16 8k;
gzip_http_version 1.1;
gzip_types
application/atom+xml
application/javascript
application/json
application/rss+xml
application/vnd.ms-fontobject
application/x-font-ttf
application/x-web-app-manifest+json
application/xhtml+xml
application/xml
font/opentype
image/svg+xml
image/x-icon
text/css
text/plain
text/x-component
text/xml
text/javascript;
# Cache static files
location ~* \.(ogg|ogv|svg|svgz|eot|otf|woff|mp4|ttf|css|rss|atom|js|jpg|jpeg|gif|png|ico|zip|tgz|gz|rar|bz2|doc|xls|exe|ppt|tar|mid|midi|wav|bmp|rtf|swf|webp)$ {
add_header "Access-Control-Allow-Origin" "*";
access_log off;
log_not_found off;
expires max;
}