What you should do:
- use the third person for formal invitations: “Mr. and Mrs. John Smith/request the pleasure…” (Mr. and Mrs.” being the parents of the bride.) For less formal invitations - and this is still considered radical by etiquette gurus - you can use the first person plural, which seems more natural if the couple is hosting the wedding: “We invite you to celebrate our wedding,” etc., with your names on the last line.
- use the phrase “request the honour of your presence” for a ceremony in a house of worship; for a ceremony in a secular venue, use the phrase “request the pleasure of your company.”
- be consistent in your spellings. If you opt for the British honour, put the u in favour. There’s no reason to go British: If you’re going for a contemporary style, honor and favor have a cleaner look.
- spell out numbers in the date and year (“the twenty-fifth of September, two thousand and ten”), but not in addresses.
- spell out numerals in times. For weddings on the half hours, write “half after five o’ clock,” not “half past five” or “five thirty in the afternoon.” Rather than “A.M.” or “P.M.,” a formal invitation should read “in the morning.”
- titles for medical doctors (but not PhDs) are generally included, both the parents and for the couple. On a formal invitation, “Doctor” should be spelled out, though for fit purposes the abbreviated form is fine. If one parent is a doctor, list that parent first; if both are, use “The Doctors Smith.”
- for Jewish weddings. invite guests to the marriage of the bride “and” groom, not of the bride “to” the groom.
- capitalise the first word of the invitation and all proper nouns. Capitalize any line that stands alone if it would be the first line a new sentence - “Black-tie” and “Please respond,” but not the “and” you might use between clauses.