You have been employed at this company for quite a while and feel that your pay is no longer commensurate with the position. Pay increases are not on a scheduled basis. How and when do you go about asking for a raise?
Do your homework:
Has the company been doing well enough that a pay raise could reasonably be requested? Have you recently completed a difficult assignment, or taken on more responsibility?
After deciding that you really have earned an increase, write and rehearse an agenda:
List your accomplishments, mention if your responsibilities have increased, additional tasks you have taken on, and projects you have headed successfully. You might want to consider typing up and printing a copy for your boss so they can look it over and discuss with other supervisors if needed.
Dress the part:
Looking polished and professional can't hurt, and will help you feel more confident.
Have other options up your sleeve:
A rejection could make an opportunity to make another proposition. Work from home one day a week, a new mobile phone or laptop for work, attend a conference or industry event you are interested in - your boss may be more likely to say yes to a smaller request if he has to say no to a big one.