How do you negotiate a salary?

[Ideal08]

My question this time is just a little bit different. Have you ever had to negotiate a salary for a new position? This is something I've never done, but I want to know how to do this. If a position is offered to you, and you think you deserve more money, how do you communicate that to the potential employer? What if you already work for the company and are getting a new position, how do you negotiate the new salary?