You open the mail and are excited to spot the colorful, thick, nicely designed envelope that could only hold one of two things, your birthday card from Grandma or a wedding invitation. You slice it open to find your invitation and memorize all the details, mark it on your calendar and post the invite on your fridge.

But wait, you forgot to fill out the R.S.V.P. card and the couple needs it returned by next week. You take it back off the fridge and stare at it, unsure about how to fill it out. Don’t worry, Dawn Jackson, a wedding planner from Minneapolis, lays out the following rules for R.S.V.P. etiquette.

1. Read Carefully. Make sure you read what the couple is asking for carefully. They’ll usually ask how many people are coming and what everyone wants to eat, but sometimes the R.S.V.P. card can have hotel options or other special requests.

“Couples use R.S.V.P. cards as their primary communication source between themselves and their guests before the wedding,” Jackson said. “It’s a medium that allows couples to ask guests for special things like song requests or kids meals.”

2. Only R.S.V.P. for invited guests. Make sure you read the envelope the invitation was mailed in. It is only safe to assume that the people’s names written on the envelope are invited to attend.

“Typically an invite will say Mr. and Mrs. Smith or Mr. Smith and Guest. Don’t assume that you can automatically bring a guest or your kids,”  Jackson said.

Katie Heineman, a newlywed from Minneapolis, got married Sept. 4. She had troubles with her guests because a large amount of them R.S.V.P.ed for more guests than were invited. She had a small venue and had to call some of her guests and ask them not to bring their families because there wouldn’t be enough room for them.

“It was really frustrating,” Heineman said. “It was like no one read who was actually invited. I had a family where we only invited the parents and they responded they were bringing their three daughters plus their daughters’ boyfriends. It got to be ridiculous.”

3. If you’re unsure, ask. If anything on the R.S.V.P. card is unclear to you or you’re not sure how to respond, ask the couple right away.

“It’s a lot easier for couples to clear up questions when they send out invitations, rather than waiting to get a wrong response or have to follow up with multiple families,” Jackson said.

4. Be clear. Make sure everything you write on your R.S.V.P. card can be read clearly. This includes checking boxes and any writing. Also, make sure you have your name on the card.

“I had a few responses that I had to spend a few minutes on trying to figure out what they meant,” Heineman said. “I also had a few that didn’t have names and had to do process of elimination just to figure out who they were.”

“It’s important to make things easy for the couple,” Jackson said. “They’re getting a lot of responses and it’s just the polite thing to do.”

5. Reply, and do it on time. The most important thing about filling out R.S.V.P. cards is that you actually fill it out and send it back on time.

“If you don’t R.S.V.P. and show up, don’t expect to eat or have a seat,” Jackson said. “It’s always going to happen, but it’s still always rude.”

It’s important to remember that once a couple gets their final guest count, their food order and seating chart are put in place. Late replies mean the couple has to re-do all this work.

“Couples usually give plenty of response time,” Jackson said. “It’s just plain rude not to reply within that time period.”

The next time you feel that exciting rush of opening a wedding invitation, don’t fret about the R.S.V.P. card. Just follow the simple etiquette rules and you’ll make the entire process easier for you and the happy couple.