prevent post submission

Question

I'm using a meta-box for custom post type. I have three problems:

1. WP seems to run the function that I attached to the "save_post" action, every time a new post is opened for editing or reloaded. Is there a way to prevent it from running?
2. WP saves the post even when I add "return false" after validation fails. Is there another way of doing it?
3. how can I validate the built-in WP title field? (I assume it is sent as $_POST['something'])

TIA for your help.