I am working in a pvt company.I want to give a letter to my boss for increasing my salary.?

Do it immediately. What are your achievements and the benefits derieved by the company should be in the first paragraph. Your commitments and the future involvement through which the company is going to be benefitted is to be in the second paragraph. In the third para ask for an increase in return for the above. Be genuine in all the above, otherwise it will worsen the situation. Best of luck. do not bother about the language. The content matters and not the frills.