If you want to improve your GTmetix score for two things – Add Expires Headers and Leverage Browser Caching then you can simply copy the following codes and add it to your .htaccess file. You would not need any plugins to do so.

Here are other tutorials to improve your GTmetrix Score:

• For Defer Parsing of JavaScript: Click  here
• Cache configuration as recommended by GTmetrix: Click here
• To serve Scaled Images & Optimize Images: Click here
• Loading jQuery from the Google CDN: Click here