I have a love/hate relationship with Christmas style (I know, it's blasphemous). I love pretty, classic decorations, but the cheesy, over-the-top stuff I could live without. A foolproof way to look festive without embarrassing yourself: tartan plaids (or as my friend Jeanne cheerily calls it, "Christmas plaid"). Some Christmas plaid for everything on your list:
For trimming the tree and addressing Christmas cards, a tartan shirt.
For parties and cocktail hours: fancy pants (in regular, petite, and tall)!
For your tree: a tartan Christmas tree skirt. (I've been looking for a simple tartan tree skirt for YEARS. I'm so excited about this one!)
For making any boring outfit holiday-party-appropriate: a darling plaid clutch.
And finally, for your gifts: tartan wrapping paper.