Aanhef: dear = formal(ish), hi = informal
Afsluiting: kind regards = formal, cheers = informal
While writing: think without contractions. Denk werkwoorden voluit. Wil je "you are" zeggen, denk dat dan eerst voluit, maak er daarna "you're" van
Think about: punctuatioin, paragraphs, using every element, synonyms.
Please, lie to me. Using made up situations makes you more creative.
Practise by using "word coach" simply type into google and it appears at top of the page.