resources :photos do
  member do
    get 'preview'
  end
  collection do
    get 'dashboard'
  end
end
This creates the following routes in addition to default 7 RESTful routes:
get       '/photos/:id/preview',          to: 'photos#preview'
get       '/photos/dashboards',           to: 'photos#dashboard'
If you want to do this for single lines, you can use:
resources :photos do get 'preview', on: :member get 'dashboard', on: :collection end
You can also add an action to the /new path:
resources :photos do get 'preview', on: :new end
Which will create:
get       '/photos/new/preview',          to: 'photos#preview'
Be mindful when adding actions to your RESTful routes, probably you are missing another resource!