Here are some mistakes that you should avoid in writing task 1 of the GT test:
- The main purpose of the letter isnt clear.
- You didnt cover all of the points.
- You wrote too much about one point, and neglected the others.
- You didnt separate your paragraphs clearly.
- You didnt get the tone right (formal or informal).
- The letter doesnt flow well because ideas are badly organised.
Avoid these mistakes, and you are on the way to writing a good letter!