Last week I told you what not to bring. Here's what you should do when you're celebrating the season:

If you're a party guest...

Don't be trash.Show some class.
Don't go empty-handed. A bottle of wine or some baked goods will do nicely. This is how you express appreciation for the invite.
No one likes a Mopey Mabel. Mingle.
Don't expect the host to hold your hand, and don't follow him or her around. And if you are a Mopey Mabel? Don't you dare bitch about the party afterward.
Keep your thoughts on Afghanistan to yourself.
Be safe with the chit-chat. Avoid politics, sex, and money as table topics.
Play nice. Go along with the theme, if there is one.
If it's a tree-trimming party, don't grouse like Grampa Fred about how much you detest pagan symbolism while the other guests enjoy themselves as they place tacky crap on the Evergreen. Don't like it? Stay home.
So nice of you to stop by, rude-ass.
If you're party-hopping, be equitable about it, or skip one party altogether.(Best to do the latter.) No host likes to feel like her guests are leaving for a "better" party. When you RSVP, let the host know you'll need to leave early, if you must feed your insecurity by demonstrating how popular you are.

If you're a host...

Your guests are not your personal wine delivery service.
Know the rules of "Bring Your Own." BYO means the beverages are placed out and imbibed during the party. It does not mean you take the wine and stash it for your personal use later, you selfish jerk.
Um, who are these people?
Realize that unlike you, not everyone knows everyone. Especially for solo guests, nothing sucks worse on party night than standing around with a drink, hoping you'll have someone to talk to. Introduce your guests to at least a few people. Aim for those who have something in common, and state this during the introductions: "Sally, this is Jane. Jane likes to shoe horses. Jane, this is Sally. Sally manufactures horseshoes."
Your guests are not your bank.
Don't you dare ask -- in any way, or at any time -- for your guests to pay for your party. I've seen this happen on invitations, in person, and at the party -- after the food was eaten and booze drunken. Throw the party you can afford, Classless Cathy. Four frozen pizzas from Aldi and a six-pack of PBR? If that's all you can do, then that's what you do. Request for money = tacky. And no, I don't want to hear your reasons why. It's tacky, period.