This is a million dollar question; a question which a lot of people have tried to answer. Some did well and some did badly. This is because unfortunately, there is no right answer. There is no guaranteed method which will get you a raise. Do not send letter. Ask for an appointment and have it across the table. You may like to follow up the discussion with an email or formal request letter .

If it's true that we are here to help others, then what exactly are the others here for?