Use the full name in standard writing unless the person uses an initial as part of his or her name. Initials may be used in lists and addresses if appropriate.
Correct: George Smith
Correct, only in list or address: G. Smith
Correct: Robert E. Lee
(The initial is fine here because that is the name he went by.)
Social titles before a proper name are capitalized. All but Miss and Master are abbreviated and end with a period.
Social titles: Mr. Master Mrs. Miss Ms.
Mlle. Mme. M. Messrs. (Plural of Mr. or M.)
Mmes. (Plural of Mrs., Ms., Mme.)
Those social titles that are abbreviated are abbreviated only in front of names.
Correct: Mr. Smith is not at home.
Incorrect: You'd better listen, Mr.
(Mr. is not in front of name; do not abbreviate.)
Correct: You'd better listen, Mister.