Express your ideas with active sentence constructions. This will allow you to express your ideas more cogently.
Use the appropriate level of formality when writing. E.g. ‘Dear Mr./Mrs. ________,’ comes across as more formal than ‘Hi _________,’
Embed images if possible rather than attach files; especially if there are many files. It can make your email easier to follow.
Always summarise the purpose of your email in the first paragraph. Organise your ideas clearly into paragraphs as nothing is more off-putting to a potential client or business associate than working with a person who cannot structure an email.
Signing off using ‘Best regards’ or ‘Kind regards’ usually strikes the balance and is often how I choose to sign off my emails to clients; it is not too formal and conveys warmth.