Why wait until after Thanksgiving? In fact, I recommend getting started on your Christmas shopping as early as possible. That will even out your budget, you will not be as likely to max out your credit cards, and you have a better chance of finding the perfect gifts. You can also find Christmas decorations online (I favor Bronners and Christmas Mouse, and there are others). Chances are you will not be able to replace certain store-bought bulbs item for item until they come in the stores after Columbus Day, but you might even find better ones.
If you have put the decorations away, you can also try to recall any shortcomings in last year's decorations. Was your Christmas tree on the wimpy side? Or, perhaps your window dressings left something to be desired? The wall in front of the kitchen sink bare? Need a wreath? Now is the time to start addressing any shortfalls, especially if you are a recent ex-witless and started last year.
Christmas trees? Some people have actually never had the chance to set one up. They were witlesses from birth, or since they were little. And, now they are 35 or 40, and just starting to realize that the Watchtower is nothing more than a Second Dark Ages cult. And now they want to set one up this year. It is not that difficult, but setting up a good one may take practice. It is more than throwing up some lights and bulbs and hoping for the best. First, you need an idea of what is, for you, the perfect Christmas tree. Single color or multi? Glitter or plain color? Clear lights or multi? Steady or flashing? Star, angel, fiber optic, bow, or snowflake top? There are so many choices that it is probably going to take at least one bad Christmas tree (and maybe several) to get it right.
For those people, I highly recommend getting some practice runs now. If you mess up, you can just take it back down, find if you need more or different ornaments, and try again until you get it right. If you wait until Thanksgiving, it is less forgiving than doing it now. And, there are people that will get it right on the first try, and those people can see if they could use more or different ornaments.
Of course, I see nothing wrong with putting the Christmas decorations up now and leaving them up if you want them up all summer long. Some people actually like Christmas decorations up most or all year, and others want a hounder repellant. Whatever suits your personal tastes. However, I do not recommend leaving a fresh cut tree or cut evergreen branches up all summer long because they will dry out and make quite the mess.