Insert message on post-new.php

I am trying to insert a message/notification into admin when a user is adding a new post as seen here – http://screencast.com/t/YJnBEtNmma

I’m not sure if the action below is the correct one to hook into or not.
add_action (‘post-new.php’, ‘insert_custom_message_for_new_posts’);

I want to provide a notice to any user/any level to provide a quick instruction.