Usually a formal wedding invitation comes with a preprinted RSVP card. A stamped, addressed envelope is also provided. Remember to reply as quickly as you can using the provided formal RSVP card.
Should the invitation come with a blank RSVP card, you should try to reflect the formality and style of the invitation. You should complete this by hand and refer to yourself in the third person. This is customary. Indicate whether or not you will be attending, such as:
Mr. And Mrs. John Jones Accepts with pleasure (or regrets that they are unable to accept) The kind invitation of Mr. And Mrs. Alan Jones For Friday, the fifteenth of May
If no card was provided, you can find response cards at any stationery store. Fill out this card as described above.