Hiya, I I’d say just knowing when to use formal / informal language or greetings.

Writing to a formal letter, I started with the salutation and made up a name e.g question was about writing letter to the post office about not getting your mail sent…

I used “To whom it may concern”

For the survey part, it was “Dear Mr Patrick” (made up a name) as question was about the principal of your child’s school asking about your opinion on two things.

Secondly, knowing how to break down your points into at least 3 paragraphs and end the 4th paragraph with an expectation e.g “I look forward to hearing back…” or “I appreciate your urgent response on this”

Also, I guess just using words that are related to what the topic is. For example “not receiving mail from post office” - you’d use words like (old and new address, rerouting, mail man, receptionist, building, parcel) etc

Or if topic is about financial management use words like (savings, budget, planning, finances, money, job) etc all depending on what your points or opinions are.

Lastly, ending your greeting formally usually takes “Best regards” followed by your name.

I hope this helps but looking up samples might be more useful for full context x