I'm not happy with my present salary, I asked to my boss but he did not give, there is dirty politics in my present company. So need to resign, need a good letter, so that they will know the reason. Maybe they will give increment.

Please help me

Unless you have another job lined up, I'd keep this one, as frustrating as it might be, until you have something better to go to. When leaving, take the high road, and if asked, tell them you found a place that pays better. You're not going to extort a higher salary by threatening to quit, you'll only be shown the door quickly and burn all bridges re: references and the like.

With my experience (10+ employers over a 30 year career) you will not get increment (excrement is more like it)

If it is time to go, write the letter, make it short and sweet, but DON'T burn any bridges. You may never darken their door again, but if a future prospective employer talks to them (even unofficially), you may regret your "F off letter".

It's a HUGE mistake on your part to put "reasons" in a letter of resignation. Just resign, period. If you must discuss "reasons" do it verbally.

I quit !!!