Resignation letters are generally one of the last communications from the employee to the organization or company.
It is important to keep it positive or neutral, as it would be in the records of the company.
The letter must be brief and to the point. The letter must include the effective date of resignation, the post from which you wish to resign and also the last date of working in the organization. The Sample Resignation letter would be one such example.
The letter may also include a thanking line for the opportunities provided by the company. It is important to leave on a positive note, without burning the bridges, as it were. This would not only help in garnering a reference in the future but also help in networking in the future, if need be.
It is good to give a valid reason for tendering the resignation as it would help the employer or the organization understand your reasons for leaving.
If your resignation is because of a genuine complain, it could be formatted on the lines of the Sample Resignation letter with complaint.