For casual ceremonies, the sky is really the limit as to style. But most weddings follow a certain set of formalities in their invitations. Here is a template for a normal wedding invitation:

         Mr. and Mrs. John Doe
   request the honour of your presence
    at the marriage of their daughter
              Kathryn Marie
                   and
          Mr. James Henry Smith
     on Saturday, the tenth of July
         two thousand and five
            at seven o’clock
          First Baptist Church
            222 Ellerbe Road
              Paris, Texas

As for a formal wedding template, there are some rules of wording that are appropriate:

1. Spell out every word, even the date and year. Street, not St. Road, not Rd.

2. Use Roman numerals in titles, such as David Kenneth Williams III. Do not use "3rd" or "third".

3. For weddings in a church, say "request the honour of your presence". For non-religious weddings, say "request the pleasure of your company".

4. Write out full names. Do not use initials.

You can copy and paste this template onto your word processor for easy guidance:

       (the name of bride’s parents/parent)
        request the honour of your presence
         at the marriage of their daughter
               (the name of bride)
                      to
               (the name of groom)
                on (weekday name),
    the (day of month, spelled out) of (month)
           at (time, spelled out) o’clock
          (name of church or building)
          (address of church/building)
           (city, state of ceremony)

Optional:

        Reception Immediately Following
                      At
             (name of location)

Directions to the reception hall can be given at the wedding or on a separate card in the invitation envelope.