PHP Environment

see here: http://www.drupalcommerce.org/questions/8356/ajax-http-error-occurred-http-result-code-500

vim /etc/php5/apache2/php.ini 

max_execution_time = -1 (default is 60 seconds, -1 is unlimited)
max_input_time = -1
max_input_nesting_level = 300
memory_limit = 256M

Download & Extract

You can download the lastest Commerce Kickstart here: https://drupal.org/project/commerce_kickstart

cd /var/www
wget http://ftp.drupal.org/files/projects/commerce_kickstart-7.x-2.12-core.tar.gz
tar xzf commerce_kickstart-7.x-2.12-core.tar.gz
mv commerce_kickstart-7.x-2.12/* .
rm -rf commerce_kickstart-7.x-2.12 commerce_kickstart-7.x-2.12-core.tar.gz

Requirements

cd /var/www
mkdir -p sites/default/files
cp sites/default/default.settings.php sites/default/settings.php
chown -R www-data:www-data sites

Install guide

Go to http://your-server-ip/ , you will see the WELCOME SCREEN.

If you see the welcome message, Congrats! Follow the guide.