This is for sure not an exact science, but this is how I have settings - in generel it has brought first page view from 12 secs to 6 secs.

Notice my Confluence is mainly for public viewing over the Internet; I would never use these settings in a Company Confluence; there is for sure some risks for "wierdness", especially when editing pages.

        CacheQuickHandler off
        CacheLock on
        CacheLockPath /data/apache-cache
        CacheLockMaxAge 5
        CacheIgnoreHeaders Set-Cookie

        CacheDisable /pages/editpage.action
        CacheDisable /rest
        SetOutputFilter CACHE
        AddOutputFilterByType DEFLATE text/html text/plain text/css application/javascript application/rss+xml text/xml image/svg+xml image/jpeg image/jpg image/png

        <FilesMatch "\.(ico|pdf|flv|jpg|jpeg|png|gif|js|css|swf)$">
        Header set Cache-Control "max-age=3024000, public"

		<Location /s>
        <IfModule mod_expires.c>
        ExpiresActive on
        ExpiresDefault "access plus 30 seconds"
        ExpiresByType text/html "access plus 15 days"
        ExpiresByType image/gif "access plus 1 months"
        ExpiresByType image/jpg "access plus 1 months"
        ExpiresByType image/jpeg "access plus 1 months"
        ExpiresByType image/png "access plus 1 months"
        ExpiresByType text/js "access plus 1 months"
        ExpiresByType text/javascript "access plus 1 months"

        <IfModule mod_disk_cache.c>
        # "/s" is where Confluence serves "static" stuff. Instruct Apache to cache it:
        CacheEnable disk /s
        CacheDirLevels 2
        CacheDirLength 1
        CacheMaxFileSize 2000000
        CacheIgnoreHeaders Set-Cookie
        CacheRoot "/data/apache-cache"

Another thing is to disable Add Ons that are never used, even though the add on is not used on pages, often some ressource as Javascript or CSS is actually downloaded with each page.