Here are some helpful tips:
For guests who don't RSVP and show up anyway: While you should make contact ahead of time with those who don't respond, don't make a big fuss of it on your wedding day if someone shows up who didn't RSVP. Yes, it's rude on their part, but simply ask a trusted friend or staff member to find them a seat and let them stay. The caterers typically prepare about 10% more food than required so it should not be a big problem.
For guests who show up with their children: A gentle way to deal with this situation is to have the family table off to the side or back of the reception area. That way if the children are disruptive, their parents can whisk them off quickly. Better yet, when you send out the wedding invitation, provide the name of reputable babysitter in your area who is willing to accommodate parents who want to attend the wedding.
Your friend's significant other is now her ex: This can be incredibly awkward but happens more than you might think. Etiquette says that if the invitation is addressed to your friend and a guest, she is free to bring whomever she chooses. However, if you address the invitation to your friend and her significant other by name, technically they're both on the guest list. If they're no longer together, you should allow her to bring someone else. You may want to have some spare place cards on hand with the word, "guest," written on them, just in case this happens.
Your parents want to invite all their friends but you want a small gathering: He who foots the bill has the power. If your parents are paying for the wedding, you certainly should consider whom they'd like to invite, however, it's still your wedding. Have a private and honest discussion with your parents if you are uncomfortable with their choices. Try to reach a reasonable compromise.
Never include registry information in your invitation: This is outright tacky and a big no-no. People will usually ask you directly, or ask a parent or other family member where you are registered. It's fine to list this information if you have a wedding website.
Asking for money versus a gift: It's becoming more common nowadays for couples to request money instead of gifts, particularly if they just moved into a new home, want to go on an exotic honeymoon, or if they have been married before. Guests may either choose to give money or a gift, depending on their financial situation.
The appropriate wedding invitation and RSVP timeline: Save-the-date cards are best sent approximately four to six months before the wedding. Invitations should be sent approximately five to six weeks before the wedding. The RSVP date should be two to three weeks before the wedding. Thank-you notes should go out as soon as possible, but try not to wait any longer than two months after the wedding. Handwritten thank-you notes are still the best way to go even in a digital world.