Remove modules
Apache include many modules that are enabled, and you may not be needing all of them, disable the ones you do not need. (By default in CentOS when you install Apache, over 50 modules are loaded.) This will help speed up Apache. The modules that are loading are listed in /etc/httpd/conf/httpd.conf and the line begins with the word LoadModule, as in:

LoadModule auth_basic_module modules/mod_auth_basic.so


For instance if you don’t use LDAP to authenticate with Apache, you can disable the authnz_ldap_module module.
If you are unsure about disabling an Apache module whose name is perhaps not self explanatory, you can take a look here http://httpd.apache.org/docs/2.2/mod/ for a more detailed description.

DNS tunning
Each DNS lookup takes up time, so make sure that Apache is not doing hostname lookups, you can enable this feature with the following directive ‘HostnameLookups Off’. This is normally off by default.

Don’t use htaccess if there is no need to
Use ‘AllowOverride None’, since allowing override will force Apache to look for .htaccess file, which you may not be using. This will speed up Apache, since it’s one less thing that Apache has to do before serving content.

Avoid content negotiation
When you access the root directory of a web server, Apache usually looks for an index file which is basically the ‘home-page’ of a web server. This file can have various names such as index, index.html, etc. You can specify the exact filename so that Apache does not have to look for different files. So replace ‘DirectoryIndex index’ with ‘DirectoryIndex index.cgi index.pl index.shtml index.html’

How do you improve Apache’s performance? Share your comments in the blog.

Reference
http://httpd.apache.org/docs/current/misc/perf-tuning.html