Formal and informal vocabulary

Dear students
I have entered some examples of formal and informal words to our blog. When we write to people we contact for education, business or other formal matters, we prefer to use formal vocabulary. When we write to friends and family, we prefer informal vocabulary.
For example when we are doing the following, we prefer to use formal language:

•          filling in application forms
•          making reservations
•          writing a job application
•          writing a CV
•          writing a personal statement
•          writing e-mails of letters to our business contacts
•          making requests or enquiries from our professors/teachers via e-mail

On the other hand, when we are doing the following we use informal language:

•            contacting friends and family
•            writing to fiends to plan leisure time activities  
•            writing to friends to share recent news
•            writing invitations to friends and family

When you know the difference, it is easier for you to choose vocabulary and language.