The first thing that I need to do is download the Omega theme and the Omega Tools and LESS modules, and then to enable both modules. I'm doing this using Drush, but you can of course do this via the admin interface at admin/modules.
$ drush dl less omega omega_tools; $ drush en -y less omega_tools
With the Omega Tools module enabled I get the drush omega-subtheme command that creates my Omega subtheme programatically. Using this command, I'm creating a new subtheme, enabling it and setting it as the default theme on my site.
$ drush omega-subtheme "Oliver Davies" --machine_name="oliverdavies" --enable --set-default
By default, four stylesheets are created within the subtheme's css directory.
The first thing that I'm going to do is rename
$ mv css/global.css css/global.less
Now I need to find all references to global.css within my oliverdavies.info
file. I did this using
$ nano oliverdavies.info, pressing
Ctrl+W to search,
Ctrl+R to replace, entering
global.css as the search phrase, and then
global.less as the replacement text. After making any changes to
oliverdavies.info, I need to clear Drupal's caches for the changes to be
$ drush cc all
I tested my changes by making some quick additions to my global.less file and reloading the page.
If your changes aren't applied, then confirm that your global.less file is enabled within your theme's configuration. I did this by going to admin/appearance/settings/oliverdavies, clicking on the Toggle styles tab within Layout configuration and finding global.less at the bottom of Enable optional stylesheets.