How to make your writing more formal?

While communicating with business people, the language you use must be consistently appropriate in style and tone.

The following are the basic features of formal writing.

• Write all verbs in full. Do not use contracted forms like don’t or can’t.
• Do not use abbreviations such as info (for information) and asap (for as soon as possible).
• Limit the use of passive voice. 
• Watch your vocabulary. Certain words are considered informal. Examples are: fix, begin, start, OK, thanks, etc. Avoid them in formal writing. Instead, use words like repair (for fix), commence (for start/begin), in order / all right (for OK) and thank you (for thanks).
• Avoid informal intensifiers like really and so. Instead use more sophisticated ones such as extremely, highly, entirely, etc.
• Limit the use of phrasal verbs. As far as possible avoid using them, but if that is not possible limit their use. It is usually possible to express the same idea using standard verb forms.
• Certain discourse markers are considered informal. Avoid using them. For example, write incidentally instead of by the way.
• Do not leave out words. Ellipsis is not acceptable in formal writing. Write ‘I hope to see you soon’ instead of ‘Hope to see you soon.’

Read more at http://www.englishgrammar.org/writing-formal/#t6FZvsTQzSfBOrIF.99