One way to write an effective two-week notice is to be brief. The employer does not need to know anything beyond the specifics of when you plan to cease working for the company, and a brief letter reduces the chances of saying anything negative about your co-workers.
The beginning of an effective two-week notice contains all relevant contact information and employee specifics. The beginning should have your name, address, phone number, email address, and the date of the letter.
The letter itself should begin formally, with the word "Dear" followed by the first and last names of the relevant supervisor. The first sentence should simply announce that you are resigning your position from the company, effective two weeks from the date provided in the letter.
Optionally, include a middle paragraph explaining that the decision to leave the company was not easy for you to make and that you found your time working at the company to be very rewarding. Tell your supervisor that you enjoyed working for her and working as part of a dedicated team.
The final paragraph should thank the supervisor for the opportunities for professional growth she gave you. Wish the company luck, and offer your assistance as the company transitions by offering your role to a new hire. End the letter by writing "Sincerely," and signing your name underneath.