It's not a question of "polite." It's business, and the most valuable persuasive speech you'll probably make at work.
- Find out what the industry standard pay is in your area, and have this information available when you talk to the boss
- Make sure the boss has time to speak with you.
- Make your case clearly, succinctly, and non-emotionally. Convince your boss you're *worth* more, not just that you want more.
- Be ready to give the boss time (chances are, he/she can't make an official decision right on the spot), but set a deadline when you'll check back with him/her to follow up.