Informal Party Etiquettes

Etiquettes to be followed even at an Informal party:

RSVP to let your host know within the specified time whether you're coming or not. If you're not sure you can make it, at least acknowledge the invitation, saying you'll let them know as soon as you can. Then do it.
Make a courtesy Call and offer to help the host with preparations or ask if there is anything you can bring, when appropriate. If you're asked to bring something, do it without fail; your host is counting on you.
Arrive right on time for a dinner party and no more than 30 minutes late for a cocktail party. But never arrive early and surprise a host that may be making last minute preparations and not be ready for you. Never accept an invitation and then not show up just because you don't feel like going out.
Greet your host(s) soon after you arrive.
Dress appropriately for the style of the party or theme.
If the occasion calls for a gift, bring one appropriate to the occasion.
Bring flowers only if you know your host(s) will appreciate them. They may be allergic to them or they may have their own flower arrangements to match the party decor.
Converse by all means. Smile, mingle and converse. But don't dominate all conversations; be a good listener, too. Don't leave your date alone in a corner, and don't bring your problems to the party. It's a real mood-killer. So are bad language and off-color jokes.
Eat, and especially drink, moderately. You'll only say something stupid, or spill something, or otherwise make a fool of yourself if you drink too much. (Report any spills right away so it can be cleaned before a stain sets in, by the way.) And no matter how much you love that one particular appetizer, don't hog it. Remember that dinner is dinner, appetizers are snacks. Eat accordingly, and don't come "starving" to a cocktail party.
If your young children are included in the invitation, bring them, and then watch them closely whether they have pulled dishes off the buffet table, run their fingers through the cake and sneezed all over the food at parties we've hosted.
Offer to help clean up toward the end of the party. Your host may very well decline, but on the other hand, they may appreciate not having to face it alone.
Leave at a reasonable time. Don't be the last, or at least, don't leave long after the next-to-last guest.
Say Thank You within a few days of the party, call or write a thank you note. Also, return the courtesy and invite your host(s) to a party of your own, or a barbecue, or out to dinner or just over for dessert. They'll appreciate it.
Proper party etiquette dictates that you should never arrive early, unless the host has specifically asked you to do so. Otherwise, you could end up being a hindrance instead of a help.
Don't upstage the host: If you'd like to bring food or drink, call ahead to ask what the host is serving. Then, bring something small to complement it. The larger and more elaborate the event (and the harder the host has worked), the nicer your gift should be. Always attach a note, or indicate on a tag who the gift is from. Don't let your gift remain anonymous!