The above is good advice in taking care of a natural tree. Now, to pick one out, I suggest getting one that, when added to the height of the topping you are going to use, will top just below the ceiling (or slightly shorter, if you prefer a smaller tree). The needles should not come off in great quantities when the tree is tapped firmly on the cut surface or shaken moderately vigorously (not abusively, of course). It should be reasonably dense--this is another matter of personal preference.
Keeping the tree cool until you are about to use it, or better yet cutting it at the last minute, will ensure freshness. Of course, it is not impossible that some critters might think it's time to wake up when you bring the tree in (hornets and spiders are not unheard of to be hibernating in these trees). Which problems can be avoided altogether with an artificial tree, but you will not get the real thing (you can get the real appearance, but those trees cost upward of $400).
Now, decorating it is another matter. If you are a newbie to Christmas, chances are you are going to have a wimpy Christmas tree because you will underestimate the number of ornaments and lights needed. And it's rather late in the season to mess up on this. As a reasonable estimate, a 6 foot tree is going to take anywhere from 150 to 300 ornaments to properly decorate (any less will be rather skimpy). And they can't all be the exact same, or the tree will lack personality. I suggest making the majority of them bulbs (glass or acrylic)--perhaps 50-60% of the ornaments. Then put some different shape ornaments, like snowflakes, stars, Santa Clauses, angels, pine cones, plastic wreath shapes, or whatever else you feel like adding. The good ones should be exposed--the plain bulbs can go all the way to the center for 3-D effects.
Now, to light the tree. Pre-lit is easiest, but if the lights are crap or sloppily draped on the tree, it is not really worth it. LEDs cost more upfront, but use much less energy and tend to last longer (for some reason, the green ones seem to go out first). If you do it yourself, plan on at least 600 lights for a 6 foot tree (I have seen ways to use as many as 80 boxes of 50 lights on a 8 foot tree. It has splendid results--but uses huge amounts of electricity and takes huge amounts of time to properly do it.) The lights go up first, then the ornaments, then the tinsel garland (which I recommend).
Colors matter. What I recommend is deciding beforehand if you want a color scheme and then, if so, sticking primarily to it (it matters not if you have an accent that violates it). If you like red and white, I recommend mostly red and white bulbs and garland, and red and white lights (with an occasional splash of gold thrown in for good measure). You might also use red and gold, blue and white, silver and gold, or red/gold/silver. You might also choose to have a tree of poinsettias, stars, angels, bulbs, or just whatever you see fit to put on it.
Most important is, for a 6 foot tree, you are going to need around 200 ornaments. Plan for about 300, since some might be defective, get lost, or break. Put some in the center of the tree, but save the showcase ornaments for the surface for maximum effect while preserving the 3-D effect. You need a minimum of 600 lights, preferably LEDs that save energy and last longer, for a 6 foot tree and about 1,000 for a 8 foot tree. Putting the lights into the center gives a better effect--start at the center of a branch, run the light along the branch, and [optionally] along some or all the greens on the way back (if you run it along all the greens, you will need up to 80 boxes), and then go to the next branch. You will still be able to access the center of the tree with all the lights on this way, plus it will be assured to evenly light the tree. Less than this will result in a sparsely lit or decorated tree; if that's the desired effect, so be it.