Best WordPress speed optimisation plugin I found till date, start free or subscribe for paid plans(get 5% instant discount by using IMITHEMES coupon code)
To speed up your website try these plugins/steps:
You can compress the javascript, css and HTML using this plugin:
https://wordpress.org/plugins/autoptimize/
You can also try some cache plugin like WP Super Cache plugin. Here are some recommended settings for that: http://support.hostgator.com/articles/specialized-help/technical/wordpress/wp-super-cache-plugin
And also optimize your images using this plugin: https://wordpress.org/plugins/wp-smushit/