As a general rule, there are very few workers who believe that they are over-paid. Asking for a pay rise is a tricky issue that requires tact and thought.
Bide your time and keep an eye on your boss. Never ask during busy or stressful times, before a holiday, after a failed project or after any redundancies.
Even with open-plan offices, always book a meeting. You can then be assured some face-to-face time and privacy.
Think about your achievements and goals. Why do you deserve more money?
Research the market and see what you could earn in a similar position at other companies, but never threaten to leave as it may backfire on you.
Give persuasive reasoning as to why a raise is deserved and ensure you give the impression of have plenty of career satisfaction.