Want to use the most awesome version of Drupal on the most awesome Drupal hosting? ;) This guide is for you!
Let's Get Started

First, head to www.acquia.com/acquia-cloud-free to set up your new site. This process takes a few minutes, but worry not; you can bide your time watching helpful tutorial videos! Once your site is provisioned, you'll be taken to the Acquia Cloud workflow page.
Upgrade PHP version (important!)

Drupal 8 requires at least PHP 5.4 in order to install, so the first order of business is switching your environments' PHP versions, which you can easily do from the Workflow page.
- Click on the triangle at the right of your Dev environment block
- Click on Configure
- Select PHP 5.5 and click Save
- Repeat the same steps for your all environments.
See Configuring PHP Settings for more information.
Add SSH keys

- Go to Cloud > Users and keys and click Add SSH key
- Give it a name, and paste in your public key file's contents.
- If you have no idea what that is ;) follow the instructions at either Mac and Unix or Windows.
Add Drupal 8 Files to Git

- Click the Git URL box in the top-right corner of the Workflow page to view a pop-up with your subscription's Git information. Your Git URL should be somethinglike:
[email protected]:webchickd8test.git
- Clone your Git repository to your local computer following the instructions in the pop-up. This command should be something like:
git clone [email protected]:webchickd8test.git d8
- Download the latest release of Drupal 8 from https://drupal.org/node/3060/release?api_version%5B%5D=7234:
wget http://ftp.drupal.org/files/projects/drupal-8.0-alpha12.tar.gz # Substitute latest version.
- Extract it to the Git clone of your site's "docroot" folder:
tar --strip-components=1 -zxvf drupal-8.0-alpha12.tar.gz -C d8/docroot
When finished, your Git repository's directory structure should look something like this:

- Now, add the new files to your site's Git repo:
cd d8 git add .
- Finally, commit/push the changes to get the D8 files onto your dev server:
git commit -m "Initial commit:
Add all the D8 code files." git push origin master
Adding and configuring settings.php

You're just about ready to go! One last thing: we need to set up settings.php, specifically for Acquia Cloud's fancy-schmancy security (that's the technical term).
- First, create your settings.php file from default.settings.php:
cd docroot cp sites/default/default.settings.php sites/default/settings.php
- Next, go to Cloud > Databases, and click the "Configure settings.php" button. It should show you some code like:
if (file_exists('/var/www/site-php')) { require '/var/www/site-php/webchickd8test/webchickd8test-settings.inc'; }
- Copy the include code, edit settings.php and add it to the end of the file.
- Finally, add and push the settings file into Git:
git add sites/default/settings.php git commit -am "Adding settings.php." git push origin master
Install away

Now you're ready to Install Drupal 8 by going to http://SITENAMEdev.devcloud.acquia-sites.com/core/install.php (NOTE: you need to go directly to the install.php script; navigating to the home page instead will give you errors).
Troubleshooting Tips

Drupal 8 is still under active development. You may run into issues attempting these steps. Here is some general troubleshooting advice.