The short practical writing task (应用文) on the gaokao English paper is an exercise in register. The marker wants to see that you can open, deliver information and close in an appropriate tone. Ambition costs more than it earns here.
Paragraph one: state your purpose in a single sentence — 'I am writing to invite you to…', 'I am writing to apply for…'. Do not warm up, and do not open with a question such as 'How are you?'.
Paragraph two: the specifics — dates, times, expectations, requests. Two or three sentences, held together with linking words such as 'firstly', 'in addition' and 'therefore'.
Paragraph three: close politely. 'I would be grateful if you could confirm your attendance.' 'Looking forward to hearing from you.' Then sign off with the correct choice of 'Yours sincerely' or 'Yours faithfully'.
Memorise a bank of ten polite formulas and rotate them across your practice letters so that no two start the same way. Markers notice.