If you have been in your job for awhile and you have been doing a good job, you may believe that you deserve more money for it. Many employers simply take their employees for granted and they don't think to give raises as often as they should. If you are known for being a consistent employee who goes above and beyond the call of duty, it isn't unheard of to ask for a raise. Generally speaking, you won't want to ask for a raise if you have been employed for less than nine to 12 months but after that you are in the clear.
A great way to ask for a raise is simply to foster open communication between yourself and your direct supervisor. If you have this open communication from day one you will find that it is a lot easier for you to share your achievements, thus making it more obvious why you want a raise when you ask for one. Of course, this requires forethought so it may be a bit late to foster satisfying communication like this before you ask for your raise.
If you believe that you deserve a raise you can choose to either ask for the raise in person or you can ask for it through a letter or an email. Depending on who you work for, there may be a preferred method of communication and you should go with that. Many individuals find that they do better asking for this sort of thing through email because they can more clearly state their thoughts, but others are more than comfortable doing this in person. Decide for yourself which works better for you and be ready to present your thoughts carefully to your supervisor.
When asking through email or in person for a raise you need to be able to cite why you deserve such a raise without coming right out and bragging about yourself. Simply state that you have been working hard and you believe that you have been going above and beyond the call of duty. When you say this you can then cite instances where you have worked harder than your job description called for, instances when you helped others, and other important issues. You don't have to go into great detail, as this may come across as bragging, but you can highlight areas where you really shine.
Simply stating the facts like this will give your supervisor food for thought, and if possible they will probably give you a raise. You need to stand ready to answer hard questions that relate to opportunity areas, or areas where you could stand to do a little bit better. Everyone has these areas, but it doesn't mean that you don't deserve a raise. Simply put the information out there, letting your place of employment know how valuable you are. The worse thing that can happen is that you will be told that you cannot have a raise at the moment, but you will definitely be put on the radar for future raises. Accept this answer graciously, but remember that you can always ask again in the future.