Mobster movies often portray a hitman rationalizing, "Nothing personal. It's just business." Methods aside, it's a good attitude to keep during the negotiation. Besides helping you focus, it can reduce stress and keep you from being overly defensive. Control yourself and you're well on your way to controlling the negotiation. Maintain the control by reigning in your emotions [source: OfficeArrow].
Remember that it doesn't have to be about money. Think about what you value most. More vacation time? Better benefit package? Nicer office? Not every employer is in a position to offer more money. Be flexible and they can more easily be flexible with you.
Another less-than-stellar reason to ask for a raise is that you're simply unhappy with your current salary. If you believe it's not fair, you'll need to justify that with solid research and approach it from that angle. Keep the conversation positive, and it'll go much easier.
If you're asked to fill a vacancy in a higher position, you're certainly entitled to adequate compensation. Even if it's not discussed at the time, it's reasonable to expect your employer to honor their side -- usually at the next annual evaluation.
Once your employer has heard your case, expect some questions. You might be asked how much of a raise you had in mind, or if you'd be willing to consider other compensation. If you haven't addressed all the ways you could contribute to the company, do not discuss money yet. Establish what your position should be and all its responsibilities before discussing financial aspects or other related benefits. For example, if it involves driving, ask about per diems and other travel expenses [source: Obringer].
Put yourself in their shoes, or even ask someone you trust to play devil's advocate. Based on your situation, think of the questions they're likely to ask you and practice your answer.
Sometimes the answer is a simple "no," which leaves two major options: accept the denial or look for other places to work. If you truly believe you're undervalued, consider finding another job. On the other hand, having the conversation with your employer sometimes improves your chances of a better review and higher salary on the next evaluation cycle.
Remember to think of this whole process as an exploration of how you can help your organization achieve more and how you can get fair compensation for your contributions wherever you are.