Getting Started

WP Rocket is the only cache plugin which integrates more than 80% of the web performance good practices even without any option activated. Its options can be defined as a bonus, since their activation is not mandatory to improve the website loading time.

So are there any recommended settings for WP Rocket?

There isn't one recommended configuration of WP Rocket that can be used on every site. Each site has different themes and plugins, so some options will work differently on one site but not another. 

The main speed boost that you get from WP Rocket is from the page caching, which is activated by default when the plugin is turned on. 

WP Rocket also adds, by default, optimal performance rules to the htaccess file (enable GZIP, browser caching etc). The other settings are designed to be optional - not required. 

We recommend trying the LazyLoad option because it helps a lot with images. In some cases, some themes/plugins don't play nice with LazyLoad, so after you turn it on, just check your site and make sure everything looks good. 
You can also read: Common Issues With LazyLoad

If you have a responsive theme we also recommend enabling mobile caching.
In our documentation you will find an in-depth description of how this option works: Mobile Caching

Files optimisation

In most cases you can also typically turn on  HTML and Google fonts minification. 

JS/CSS minification is recommended as a 'best practice', so it might improve your Google PageSpeed "grade",  but it doesn't always make much of an impact on your actual load time. If you see any issues on your site after activating these options, you probably need to exclude a file or two as we explain here: 
Resolving Issues with File Optimization

If you see any issues on your site after enabling an option, simply turn it off and clear the cache, and everything will go back to normal. If any option causes a problem only on one or two pages, you can easily disable it on a per page/post basis by using the Cache Options box on the right side of the edit screen for a post/page. 

If you are an advanced user, you may want to experiment with Render-blocking Javascript and CSS. On the Static Files tab you'll see an option for this. Again, this is something that can improve your "grade" but you always need to check if it makes a difference to the actual load time. Moving CSS and JS files around can break your site, so these options should be used carefully, if at all.
To learn more about it, check this doc: Render-blocking Javascript and CSS (PageSpeed)

If you have 3rd party content on your website (for example fonts loaded from Google Fonts or a video from Youtube), you may want to add its origin domain to the DNS prefetch option. It can be a minor boost to your loading time, since the DNS resolution will have already been made when requesting the external resources. You can watch this video to learn how to use the option: http://www.youtube.com/embed/jKMU6HgMMrA

Measuring your page load time

To see the benefit WP Rocket provides and to test the effect of different options, you should  measure your page load time with Pingdom: 
http://blog.wp-rocket.me/correctly-measure-websites-page-load-time/

The actual load time of your site is much more important than your performance "grade" from Google PageSpeed, GTMetrix etc:
Why You Shouldn't Care About Google PageSpeed Insights