i dont know how to write a letter seeking for a raise in salary. but as a guide, what made you think that you deserve a raise? the timing is also important. like for example, you have just finished a big successful project, yun, dapat gawin mong isang basis for salary increase. or i mention mo yung mga achievements mo since yung last increase. or you mention kung ano ang salary range in your specific industry based on number of years' experience. you sell your self based on your capabilities. wag yung parang nagmamakaawa ka. yun lang.