dear dipti,
while resigning from any company u should keep one thing in mind. Dont say anything negetive about the company, even if it is not a good company.
The resignation letter should be short and sweet, with a genuine reason of leaving without affecting the image of the company...
Below is the copy of one post when I searched on cite HR supporting my views:
Resignation is something which people do it for two reasons. One when you get a better opportunity where growth is perceivable and the other when you or the management cannot see eye in eye! If the resignation is for the first reason, there is no problem you can thank them for having given an opportunity to work in that organization and for having learnt many things, because of which you are ready to take more responsibilities and career enhancements.
If the resignation is because of the second reason, though you are frustrated for any reason, you cannot express them in writing the resignation letter. Very plainly you can write due to personal reasons I am resigning the job. Because as other friends has put it, the world is small and we will meet sometime or the other. Instead of turning this side and that side, not able to face the other person, it is better we resign and leave without any rubbings. I am sure, with my experience, the other person will remember you and will have better words to speak about you in the later days. This will all happen because of the EGO which every one of us have. But while leaving, in polite way, you can explain that you are at no fault and also you may tell the circumstances that lead to this resignation.
I hope this reading will be beneficial for you.