Things you may want to do before you install
Set a static IP address and Host name
First things first update and upgrade the image by running the commands
sudo apt-get update && sudo apt-get upgrade
depending on when you last did this and how old your image is this may take 30 minutes or more.
So now on to installing apache
sudo apt-get install apache2 php5 libapache2-mod-php5
You may have noticed a couple of errors when installing, to fix you need to run the following commands
sudo groupadd www-data, then sudo usermod -g www-data www-data.
Now restart the apache web server by running the command sudo service apache2 restart
To enable htaccess files you must modify the config files, like so:
Type sudo nano /etc/apache2/sites-enabled/000-default and hit Return / Enter.
You'll see a line like the following:
"AllowOverride None" - change this to "AllowOverride ALL".
(Note that "AllowOverride None" appears in a couple of places. You want to update the one under <Directory /var/www/>)
To save your changes hold the Ctrl button and press the "x" key, then press "y" when prompted and hit Return / Enter.
Now restart apache with sudo service apache2 restart.
And that should be it :-)
You can check that its all working by opening up a web browser and entering the url: http://raspberrypi/
Alternatively from the pi itself go to http://127.0.0.1 or http://localhost