Omega theme installation and subtheme creation on Drupal 7

Get into the folder of drupal 7 themes sites/all/themes a write command

drush dl omega

Than into the folder of modules sites/all/modules and write

drush dl omega_tools than install omega modules

drush en omega_tools -y allow the omega tools

For creation the subtheme, you have to write

drush omega-subtheme "Your subtheme"

drush en "your_subtheme" -y 

drush vset theme_default your_subtheme

That is all.