For many people, this is the scariest conversation they can imagine having with their boss. They prefer to avoid the situation and just accept the standard annual pay increase (if any). But if you've been adding value to the company, you deserve better than that.
Your annual performance review is the ideal time for this discussion because it gives both parties a chance to prepare for a mutually satisfactory outcome. Just showing up at your supervisor's door and demanding a raise is much more likely to get a knee-jerk no, if only because your supervisor isn't authorized to make that decision on his/her own.
Prepare your case.
Like a lawyer getting ready to go into court, plan out your arguments as to why you deserve a raise, and back them up with supporting evidence. This evidence could be production or sales quotas you've exceeded, compliments you've received from customers, projects you've completed successfully, ways you saved the company money or brought in new...