Expires headers tell the browser whether they should request a specific file from the server or just grab it from the cache. It is advisable to set static content's expires headers to something far in the future.
If you don't control versioning with filename-based cache busting, consider lowering the cache time for resources like CSS and JS to something like 1 week. Source
<IfModule mod_expires.c>
ExpiresActive on
ExpiresDefault "access plus 1 month"
# CSS
ExpiresByType text/css "access plus 1 year"
# Data interchange
ExpiresByType application/json "access plus 0 seconds"
ExpiresByType application/xml "access plus 0 seconds"
ExpiresByType text/xml "access plus 0 seconds"
# Favicon (cannot be renamed!)
ExpiresByType image/x-icon "access plus 1 week"
# HTML components (HTCs)
ExpiresByType text/x-component "access plus 1 month"
# HTML
ExpiresByType text/html "access plus 0 seconds"
# JavaScript
ExpiresByType application/javascript "access plus 1 year"
# Manifest files
ExpiresByType application/x-web-app-manifest+json "access plus 0 seconds"
ExpiresByType text/cache-manifest "access plus 0 seconds"
# Media
ExpiresByType audio/ogg "access plus 1 month"
ExpiresByType image/gif "access plus 1 month"
ExpiresByType image/jpeg "access plus 1 month"
ExpiresByType image/png "access plus 1 month"
ExpiresByType video/mp4 "access plus 1 month"
ExpiresByType video/ogg "access plus 1 month"
ExpiresByType video/webm "access plus 1 month"
# Web feeds
ExpiresByType application/atom+xml "access plus 1 hour"
ExpiresByType application/rss+xml "access plus 1 hour"
# Web fonts
ExpiresByType application/font-woff2 "access plus 1 month"
ExpiresByType application/font-woff "access plus 1 month"
ExpiresByType application/vnd.ms-fontobject "access plus 1 month"
ExpiresByType application/x-font-ttf "access plus 1 month"
ExpiresByType font/opentype "access plus 1 month"
ExpiresByType image/svg+xml "access plus 1 month"
</IfModule>
Remember that for most rules you must have the RewriteEngine on rule in your .htaccess file!!!
Please remember to double check and verify any rules that you use. If you do not understand a rule please consult someone who does. Or if you are new, please take time to learn the basics of .htaccess. We accept no responsibility for your use of these rules - use them at your own risk. Please get in touch if you want us to add a rule!