This document gives you all the needed steps to deploy the [LESS css pre-processor] (http://lesscss.org/ "LESS css pre-processor") on your Drupal installation. The following given commands assume that you have Drush installed.
To achieve this, you only need to go into your Drupal installation folder and type:
drush dl less to download the LESS module
drush en less -y to enable the LESS module
To have a working less installation, you will need to go to your "DRUPAL_ROOT/sites/all/libraries" folder (if the libraries folder does not exist yest, just create it), and to extract the Lessphp library into it. You should have something like *DRUPAL_ROOT/sites/all/libraries/lessphp/lessc.inc.php".
In your Drupal back-office, go to the following URL "/admin/config/development/less", then check "LESS developer mode" and uncheck "LESS watch mode". These settings will allow Less to regenerate files on every request. Please also make sure that your "files" directory has sufficient permissions.
Note: Do not forget to turn off the developer mode when putting your website on the production environment.
You are now ready to use LESS with Drupal 7.x.