Apache

* Newer RPis: install apache:
sudo apt-get install apache2

* Older RPis: install apache:
sudo groupadd www-data
sudo apt-get install apache2

* edit index.html page:
sudo nano /var/www/index.html

PHP and MySQL

* install PHP packages:
sudo apt-get install php5 libapache2-mod-php5 mysql-server mysql-client php5-mysql

* create firsttest.php script
sudo nano /var/www/firsttest.php

<?php
  phpinfo();
?>

* install phpMyAdmin:
sudo apt-get install phpmyadmin

* add pi to the www-data user group and grant write permissions:
sudo usermod -a -G www-data pi
sudo chmod 775 /var/www

* add permission to work as user other than pi (substitute user name for <Username>)
sudo adduser <Username> www-data

A Leaner Approach

* remove Apache to install Lighttpd:
sudo apt-get remove apache2 php5 libapache2-mod-php5 php5-mysql

* install Lighttpd:
sudo apt-get install lighttpd

* install MySQL and include PHP as a CGI module:
sudo apt-get install php5-common php5-cgi php5
sudo apt-get install php5-mysql

* allow web server to parse PHP scripts:
sudo lighty-enable-mod fastcgi-php

* restart Lighttpd:
sudo service lighttpd force-reload

Content Management Systems

* install Joomla:
joomla.zip unzip -d /var/www
rm /var/www/joomla.zip

* change directory and file permissions:
find . -type f -exec chmod 644 {} \;
find . -type d -exec chmod 755 {} \;