1. You're not including the wedding location on your save-the-date card.
Even if you and your fiancé are from the same hometown and still live there now, there's no guarantee that the wedding will take place in that same location. Avoid having 100 people asking you, "Where's the wedding?" by including the city and state on your save-the-date (no need to put the actual venue at this stage). Many of your guests will still have to travel and possibly book overnight accommodations so give them a heads as a courtesy.
Related: Creative Photo Save-the-Date Ideas 
Photo courtesy of Wedding Paper Divas
2. You're choosing a less convenient date or time.
As weddings have grown more expensive, it’s not surprising that more couples are opting to get married on a Friday or Sunday rather than the high-priced Saturday night. But there’s a reason Saturday is the most popular day for weddings to take place — with Friday weddings, your guests either need to take the day off work, leave work early, or skip your ceremony altogether and just attend the reception. With Sunday weddings, unless it’s a holiday weekend, guests won’t be able to let loose as much as they’d like, and many will leave early to get a good night’s sleep before the work week begins again.
If you choose Friday, start your ceremony later — perhaps 7 or 8 p.m. And if you opt for Sunday, consider an afternoon ceremony with the reception ending by 9 or 10 p.m. (you can have an informal after-party back at the hotel for guests who do want to party all night).
Related: 101 Best Wedding Budget Tips 
3. You're not making clear-cut lines on who’s invited and who’s not.
There are certain groups you generally can’t break; even if you see some of your aunts and uncles a few times a month and others a few times a decade, you really should include all (or none) out of fairness.
Regarding “plus ones,” the general rule is that couples who are married, engaged, or living together must be invited together, even if you haven’t met your friend’s significant other. After that, it gets a little less clear-cut. Some couples give a plus one to singles over 18. Others decide to include dates for anyone in a relationship, while others draw the line at just couples who have been together for a year or more. Whatever you decide, consistency is key. The exception is your bridal party members — if you can swing it, allow your single bridesmaids and groomsmen to invite dates if they choose to do so.
4. You're putting a false start time on the invitation.
If you’re planning to walk down the aisle at 7 p.m., the time on your invitation should be 7 p.m. Don’t leave your guests waiting just because you want to make sure no one misses your grand entrance. Most guests know better than to show up right at the invite time anyway, so if you put 6:30 for a 7 o'clock ceremony, some of your guests could be waiting around for as long as an hour before you begin.
Photo courtesy of Wedding Paper Divas
5. You're using pre-printed labels on the invitation.
Your invitation sets the tone for your wedding — and that starts with the envelope. Now, we’re not saying you need to hire a calligrapher, but it adds such a personal touch to handwrite the addresses. Perhaps ask a friend or relative with nice handwriting to help out. Or, try this calligraphy cheat: Using a fancy font in a very light gray, run each envelope through your printer, and then trace over the printed address using a calligraphy pen. Your guests will never know your secret!
6. You're sending an invitation to someone who already told you she can’t attend.
After receiving your save-the-date, your friend tells you that she’ll be out of town and can't make it to your wedding. When it’s time to send your invitations, skip mailing one to this person — sending when you know she can’t attend gives off a “gift-grabbing” vibe.
This rule confuses a lot of brides because you’re also not supposed to invite anyone to the engagement party or bridal shower  who won’t be invited to the wedding. However, since you did extend the invite — even though you didn’t send a physical invitation — it’s acceptable in this scenario for your friend to be included in pre-wedding events.
7. You're having a cash bar.
In a perfect world, your guests won't have to open their wallets at your wedding. But you don’t need to shell out for a top-shelf open bar if that’s beyond your budget. It’s perfectly acceptable to offer just beer and wine, and it's a nice touch to add a signature cocktail  or two. If you must have a cash bar, see if you can negotiate some drink specials with your venue to lessen the burden on your guests.
Photo Credit: D. Park Photography
8. You're not feeding the band.
Vendors who will be sticking around through your reception — band/DJ, photographer, and videographer — need to be fed. Most even state this in their contracts. Check if your venue offers a “vendor meal,” which typically cost about half as much as a guest’s dinner (the vendor meal usually includes just the main course, which lowers the cost). Or, you can sometimes provide subs, pizza, or another quick meal for your vendors (ask them!). Also, encourage them to grab some food during the cocktail hour.
9. You're not take the time to greet each guest personally.
As receiving lines  have gone out of fashion, more and more couples plan to visit each table during the reception instead. What you don't know is that most couples never make it around to every table — you'll get sidetracked when your favorite song comes on or when your cousin drags you off to the bar for celebratory drinks, and before you know it, it's time to cut the cake and say goodbye. Our advice: Have a receiving line, even if it feels outdated and takes away from photo time. Think about it this way: Would you rather spend 15 minutes having a receiving line after the ceremony or spend an hour (or more!) going around to every table? Whatever you do, do not make an announcement that guests who want to see you can come join you on the dance floor — yes, we’ve heard this happen many times.
10. You have expectations for your gifts.
We all secretly hope that we’ll get those carefully-selected items on our registries or that we’ll receive enough money to make a down payment on a house. But, contrary to popular belief, wedding guests aren’t even required to give a gift — and there certainly is no minimum amount that your guests have to spend .
Also: This means that you should not include registry information with your wedding invitation. You can, however, include it with your bridal shower invite, since the primary purpose of the event is to shower the bride with gifts!
Photo Credit: Evermore Photography
11. You're skimping on bridal party gifts.
Considering that the average bridesmaid spends almost $600  between the dress, the bridal shower, the bachelorette, and attending the actual wedding, this isn’t a place where you should trim your budget. No, you definitely don’t have to match what they’re spending on you, but plan on about $50-150 per bridesmaid if your budget allows. Also, don’t forget thank-you gifts for your parents!
Related: 40+ Bridal Party Gift Ideas for Every Budget 
12. You're using thank-you cards with pre-printed messages.
Believe it or not, back in the 1950s — often heralded as a time when great care was taken toward having proper manners and etiquette — pre-printed thank-you cards were the norm. How and why did this change? Over the years, weddings have grown in size and cost; no longer do most of your guests live within walking distance to your venue. Guests are flying in from all over the world and spending more than $500 to attend a wedding . Somewhere along the line, it was decided that guests deserve a more personal “thanks” for their time and effort spent on your behalf.
Also: You don’t have a year to send out thank-you cards. You have three months, tops. And for gifts sent before the wedding, try to get your thank-yous out within two weeks of receiving the gift.
Related: The Top 10 Thank-You Note Mistakes 
Tell us: Which of these rules have you broken?