2 & 3. In lieu of exchanging gifts with friends this season, have a clothing swap. Or make an agreement to only give second-hand gifts, and then scour Etsy and local thrift stores for something truly unique. (And there's always the option of making your own mdash; hello, DIY.)
4. For your big holiday party, avoid using disposable dinnerware and rent instead. You probably don't have 48 champagne flutes. (And you might not have room for them in your apartment even if you did.) If you want to keep your party classy and save the earth at the same time, try searching for a party rental company in your area that rents glassware and dinnerware. It's surprisingly affordable (around $.50 for a wine glass at one place I checked) and many places don't have minimum orders. Plus, many companies offer delivery and pickup — and they'll wash the glasses for you.
5. If using disposables is unavoidable, you can purchase disposables that are earth-friendly and recyclable (or compostable). Another tip: if I'm buying plastic cups I always check the number on the bottom on the bottom to make sure I can recycle them later. (Many disposable cups, like those famous red Solo cups, can't be recycled in areas that won't take a 6 (like mine)).
6. Start a new holiday tradition and plant a tree with your family.
8. & 9. Turn the thermostat down a few degrees and warm yourself by the soft glow of a recycled paper fire log. (Or you can use this handy-dandy device to make your own. I'm going to be burning all my junk mail in no time.)
10. Once all the merriment is over, recycle your Christmas tree instead of throwing it away. Check for facilities in your area. If your city doesn't have a Christmas tree recycling program, Organic Gardening has a few DIY recycling ideas.