On live production:
$ RAILS_ENV=production bundle exec rails c
Create new user, and save--and you're done:
$ @l = User.new(email: 'someone@somedomain.com', shortname: 'someone', first_name: 'Some', last_name: 'One', password: 'password')
$ @l.save
For a development workflow, you can run with guard (check out the Guardfile for configuration):
$ bundle exec guard
Or you can simply run rspec:
$ bundle exec rspec