.htaccess configuration

Normally be able to enable mod_deflate module for Apache2 safely with the following lines inside your .htaccess file in your www root of your website:

<ifmodule mod_deflate.c>
	# Insert filter
	SetOutputFilter DEFLATE

	# Compress Level 9 - maximum
	DeflateCompressionLevel 9

	# Netscape 4.x has some problems...
	BrowserMatch ^Mozilla/4 gzip-only-text/html

	# Netscape 4.06-4.08 have some more problems
	BrowserMatch ^Mozilla/4\.0[678] no-gzip

	# MSIE masquerades as Netscape, but it is fine
	BrowserMatch \bMSIE !no-gzip !gzip-only-text/html

	# Don't compress images
	SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip dont-vary

	# Don't compress archives and pdf
	SetEnvIfNoCase Request_URI \
	    \.(?:exe|t?gz|zip|bz2|sit|rar|pdf)$ \
	    no-gzip dont-vary

	# Make sure proxies don't deliver the wrong content
	Header append Vary User-Agent env=!dont-vary
</ifmodule>

Virtual Host Notes

Some people argue that configuration in the VHost is better because it saves your server the disk IO of accessing the .htaccess file with every request (Note: for VHost configuration you will need to be admin of your server).
Save above rules in a file, named mod_deflate.conf and copy the file to /etc/httpd/conf.d//etc/httpd/conf.d (CentOS)

Testing

To test if mod_deflate is work, go to  http://www.whatsmyip.org/http_compression/ and we enter the whole URL to your website or stylesheet or javascript file. You should see a big green tick and the site will say the PAGE or CSS or JAVASCRIPT  is compressed.

Website Performance

Also, here a Free Website Performance Tool and Web Page Speed Analysis Enter a URL below to calculate page size, composition, and download time.