How much 'play' is there in a longtail keyword?

[wetlazer]

I am sure this is a basic concept. So please forgive my ignorance. How much 'play' is there in a longtail keyword?

For example, let us say adwords gives the phrase 'How to dance The Twist.' If I changed my phrase to 'Learn how to dance The Twist.' Or 'How to dance The Twist quickly.'

What does this do to the longtail keyword? Is the phrase the same or is it a different phrase? If you use a comma, or a period does this make a difference?

Is there a tip, technique, trick which would be helpful?

Thank you.