Asking for a raise is uncomfortable for many people, and most are usually not trained in how or when to make this request. The goal, besides getting more money, should be to keep the discussion very positive so that, even if the answer is no, you can still maintain a good relationship with the company. Before you ask, consider the salary range for your position and your track record with the company to determine how likely it is that they'll be willing to give you more money. You'll need to provide good reasons for why you should get a raise, and may want to consider additional responsibilities you can take on to make it worth the company's while.
Before asking for a raise, consider how likely you actually are to get one. If the job has a salary cap you are well below, then you have room to work with. Often, salary caps are raised after an employee has been working with a company for several years, and it can be irritating to have new, untrained employees coming into your company who are actually making more money than you. You'll want to keep this irritation at bay, however, and approach the situation logically.
It typically costs most employers more money to hire and train new people than it does to keep experienced workers on at a slightly higher salary. If you have been a good employee, with a good attendance record and job performance, it is usually in the company's best interest to retain you and increase your salary. Most companies would prefer to keep a fully trained worker than to hire someone new.
This does not, however, mean that you should threaten to quit if the request for a raise is not granted. Unless you have somewhere else to work, don't make this threat and don't treat a denied request in a negative way. It takes at least an average of five months to find a new job in a good market, so consider the downfalls of quitting. If, however, you've been given an offer from another company that is more lucrative, but you like where you are, you should make your company aware of this offer so they have the opportunity to match or beat it.
Most employment experts feel that you should ask for a raise in person. You can certainly write a short note to a boss saying you'd like to discuss your "development" in a company, and asking for a time to meet. Don't refer to your salary when making this request.
Once you've arranged a meeting with your employer, you need to have clear reasons to ask for a raise. Hold onto your performance reviews and document contributions you make to the company. Perhaps you are a great employee who hasn't missed a day of work in two years, or you have brought new business into the company. Most reasons should be directly related to how you have contributed in ways that merit additional pay. These should be calmly related to the manager in a friendly way.
You may also want extra responsibilities or an opportunity to move up in the company. Some employers can take advantage of this by offering you new responsibilities without a raise, although many people think this really isn't fair. If you feel this offer is acceptable, you may want to accept it pending a review and raise within a specified number of months. When possible, get this agreement in writing.
Once you address the subject of a raise, suggest a possible number. Make it a bit higher than what you want, but not ridiculous. Any possible number you suggest will probably be met with a counteroffer, so ask for more than you actually hope to receive. If you are experiencing financial hardship, tell an employer about this last. Unless your work is the reason for your problems, this is generally not an acceptable reason to ask for a raise.
Some employers go through several years of freezing employee's salaries, which usually means that any request for more money will not be granted. Watch for improved financial conditions and strike when the time is ripe. Your loyalty to the company for continuing to work there despite frozen salaries can be emphasized.
Getting a raise often depends on the economic conditions of the company, but if you have brought in significant revenue, you should share in the profits. If you find your employer completely dismisses you when you ask for a raise, shop around for another place to work. It is always a good idea to have a job while you look for your next, which hopefully will be a more lucrative one.