Traditionally, the bride's parents' were charged with paying for the wedding so their names would be listed as the hosts. In more formal weddings this wording is still often used, but not always. Nowadays, isn't always the case that the bride's parent's pay for everything. Sometimes it's both families and sometimes it may just be the bride and groom that foot the bill! "Together with their families..." is common; as is listing of both sets of parents in the introduction.
The invitation line is the line that requests the guests to the wedding. This can be worded many ways but is frequently seen as: "request the honor of your presence," "cordially invite you to," "invite you to join," "request the pleasure of your company," or "invite you to share the celebration." Depending on the vibe of the event, this line can be as informal or formal as you'd like.
After the host and invitation lines, the couple is listed (bride first). These names are often designed with a much larger typeface and bolder font in order to draw the attention to who this shindig is celebrating! More formal invitations list first and middle names whereas informal invites often display first names only (or maybe first and last as shown above).
Date and Time
Typically, the dates and times are capitalized and spelled out completely rather than using numbers. Example: Saturday, the twelfth of September, Two-Thousand Fifteen, at four-o'clock in the afternoon. And, again, if the invitation is more on the informal side, these phrases can be altered to "Saturday, September 12, 2015 at 4 pm." I will say that spelling out the words is the most common, however, whether the invitation is formal or not.
For well-known venues, an address is not required to be listed. Usually just the venue is listed followed by the city/state that it is located. If an address or directions are needed in the invitation, a separate insert card can be created.
Sometimes, "reception to follow" is listed at the closing of the invitation. Or perhaps, "dinner and dancing to follow." If the reception is in the same venue as the ceremony, "reception immediately to follow" is often used. Not having a dinner? In that case, writing, "cocktail reception to follow," "dessert reception to follow," or "hors d'oeuvres reception to follow" works perfectly fine as well. No kids at the reception? Stating "adult reception" is a polite way of requesting this.
If you'd like to specify a dress code, this can also be written under the reception information. Some dress codes might be: black tie, semi-formal, cocktail attire, festive attire, black-tie optional, dressy casual, or informal.
RSVP and Registry
In the case of my informal invitation above, this couple chose to list the stores in which their wedding registries are located as well as RSVP information. Even in an informal instance, I would advise having a separate insert for these categories. But to save on money for the extra paper, maybe listing it on the same sheet is more practical for you. In the grand scheme of things, it's your day. Make your own rules! :)
Happy writing, friends!