There is no such thing as too early. I have been preparing for this Christmas since last Halloween! By gradually building levels up on decorations, I am going to have my place decorated real good by this Columbus Day. Hey, I have heard of one person who was raised a Witless getting a Christmas tree up as soon as it came, in July.
If you are a first-timer, I really suggest reading the tips on how to decorate a Christmas tree on the Internet. Good Housekeeping has some really interesting tips (warning: If you use 4,000 lights, make sure they are LEDs or you are going to have fuse blowage issues since this many minis use 1,600 watts. LEDs use only 160 watts for the same number.) And, if you get an artificial tree, you still have some time to practice decorating it. First-timers might know what they want, but need some practice runs and some crappy looking trees before they get it right. If you are going to have a crappy looking tree, better now so you can take it down and set it up again until you get the hang of it.
Speaking of crappy trees, now is also the time to take inventory of your ornaments. The optimal time for that is when you take the tree down--note any missing or busted bulbs or faulty light sets, and replace them at that time. But this might be the best time for first-timers to dry-run their ornaments. First timers usually find they are skimpy on ornaments, and now is a better time to fix that problem than waiting until the day after Thanksgiving and then finding out that it is wimpy or that you can't put up the tree right. The earlier you can get these issues addressed, the better the results are going to be when it's time to set the tree up for real. And, there is nothing wrong with having the decorations up whenever you feel like setting them up!