A man should look for what is, and not for what he thinks should be. - Albert Einstein
If you want to ask for a raise, you need to do your research first. Consult the Internet, friends, and books about career and salary information. Consider recent performance appraisals connected to the job you are doing. Gather other relevant information, as well. Further, inform yourself of company policy concerning compensation. Some employers only give raises at certain times of the year, because they are limited by budget constraints. Know what you want when it comes to your career and finances. Come up with a salary range that works for you. Think about the justification for the increase, so that you have it ready to review with your supervisor.
Do not be rigid and demanding; be flexible when it comes to your career. Perhaps you would be open to extra vacation time instead of a raise. Sometimes, an alternative works well. When you are ready for the discussion, ask your supervisor for a meeting to discuss your salary. Stay collected as you present your request. Support what you say with valid factors. Do not ask for or expect an answer on the spot. Ask your boss to think about it. He or she is mostly likely going to have to discuss the issue with the Human Resources department and other managers in the company. Hope for a positive response, but do not have high financial expectations. Remember that there may not be enough money in the budget for a salary increase. Finances and careers are touchy issues. Negotiating a raise may not get the results you want, but it is good to try.