At the risk of becoming known as the Parenting Squad’s resident curmudgeon, I think it’s time I address something you may not enjoy teaching your child: good manners.

“He’s just being a kid” or “We aren’t that formal” are poor excuses for lazy parenting. Using your manners is the way you show respect for those around you, and your consideration for them. If you have taken on the responsibility of good parenting (and if you are on this website, you likely have), part of your job is teaching appropriate social behavior.   Although your family may have a very relaxed atmosphere at home, insofar as manners are concerned, kids need to know how to handle themselves in new situations. These skills will really come into play when they begin meeting scholarship committees, college admissions officers, and prospective employers. Although you may find etiquette tedious to teach, please realize that you are helping them out in the long run.
While your child is never too old to learn basic etiquette,  it certainly becomes harder to enforce as they become older.
Here are some important basics that you should consider teaching your child.
Please, Thank You, No Thank You and Excuse Me. None of these words are difficult. If you, as parents, use them, so will your children. 
Thank-You Notes. Talk about a life skill! Even preschoolers can draw charming pictures or write their names in cards. Making your own cards is also a great, inexpensive craft.   Have trouble getting started? Encourage them to write about what they enjoyed about the gift, outing, etc.  The next step, for elementary-age children, is to learn to address an envelope properly and apply the appropriate stamp. High-schoolers will need to write thank-you notes for a multitude of purposes: college recommendation letters, college admission officers’ interviews, and job interviews.  
Table Manners.   Wait until everyone is seated before you begin eating. Please do not talk with your mouth full, Junior. A child can easily learn how to set the table properly, too. The plate goes in the middle. The fork goes on the left. The knife, blade facing the plate, goes to the right of the plate. The spoon goes next to the knife. Your napkin goes under the fork. When you sit down, the napkin goes onto your lap. When you are a guest at someone’s home, thank them for inviting you, and take your plate to the kitchen when the meal is over. A great guest helps with clean-up, or at least offers.
Restaurant Manners. I know of some parents who dread taking their children out to eat. With a little preparation, you can all relax and enjoy your meal. For our toddler, I used to pack some extra ammo. I’d hit the Dollar Store and stock up on some items to keep in my arsenal – coloring books, little toys, chunky small books. This will give the little person something to do. Also, my husband figured out early on that we needed to bring some crackers or cereal to tide her over, while waiting for our meal. Some servers, at your request, will bring the child’s meal with your salads. If your server makes an effort to keep your child happy, please tip appropriately. At a very fancy restaurant, don’t be intimidated by all the silverware. The rule is easy: work your way in with your utensils. Be polite to the wait staff. You, as the parent, have an obligation to be considerate of your fellow diners. Children should not run through restaurants, and should keep their voices down. Cell phones should be turned off.
Movies and Concerts. Arrive early enough at a movie to allow time to use the restroom and buy refreshments. That way you won’t need to scoot in front of other patrons while they are trying to enjoy the movie.
Concerts are a little trickier. For a concert that features classical music, your child needs to be old enough to observe the protocol. Allow enough time beforehand to use the restroom. Explain what the usher does. Once seated it’s important to stay seated until the intermission. Unwrapping candies or talking are considered rude behavior. Also, you should explain that sometimes you do not clap until the very end of a piece.
A Firm Handshake. I mean firm, not limp. Practice with your child. 
Consistency in the use of manners, early on, will put your child at ease in social situations. Remember, your children look to you for direction and education. They want to know how to handle themselves appropriately and confidently.