In der Htaccess kann man folgendes eintragen:
Quelle: https://wpdatatables.com/leverage-browser-caching/

#
# Optimierung lt.: https://wpdatatables.com/leverage-browser-caching/
#
#Customize expires cache start - adjust the period according to your needs
<IfModule mod_expires.c>
  FileETag MTime Size
  AddOutputFilterByType DEFLATE text/plain text/html text/xml text/css application/xml application/xhtml+xml application/rss+xml application/javascript application/x-javascript
  ExpiresActive On
  ExpiresByType text/html "access 600 seconds"
  ExpiresByType application/xhtml+xml "access 600 seconds"
  ExpiresByType text/css "access 1 month"
  ExpiresByType text/javascript "access 1 month"
  ExpiresByType text/x-javascript "access 1 month"
  ExpiresByType application/javascript "access 1 month"
  ExpiresByType application/x-javascript "access 1 month"
  ExpiresByType application/x-shockwave-flash "access 1 month"
  ExpiresByType application/pdf "access 1 month"
  ExpiresByType image/x-icon "access 1 year"
  ExpiresByType image/jpg "access 1 year"  
  ExpiresByType image/jpeg "access 1 year"
  ExpiresByType image/png "access 1 year"
  ExpiresByType image/gif "access 1 year"
  ExpiresDefault "access 1 month"
 
</IfModule>
#Expires cache end
# BEGIN Cache-Control Headers

<IfModule mod_expires.c>
  <IfModule mod_headers.c>
    <filesMatch "\.(ico|jpe?g|png|gif|swf)$">
      Header append Cache-Control "public" 
    </filesMatch>
    <filesMatch "\.(css)$">
      Header append Cache-Control "public"
    </filesMatch>
    <filesMatch "\.(js)$">
      Header append Cache-Control "private"
    </filesMatch>
    <filesMatch "\.(x?html?|php)$">
      Header append Cache-Control "private, must-revalidate"
    </filesMatch>
  </IfModule>
</IfModule>
<IfModule mod_headers.c>
            Header unset ETag
</IfModule>
FileETag None