JP is the expert, but I've picked up some tricks for decorating the tree from my prop stylist friends over the years that help make the process go fairly smoothly.
Always put the lights on first, of course. We like Real Simple's vertical method for adding lights to the tree. It gives your tree an even glow, and it's easier to take down the lights later.
Instead of ornament hooks, I like to use a twist of floral wire. That makes it easier to get the ornaments deep into the tree and keeps them from falling off throughout the season. When you dismantle the tree at the end of the season, just untwist your floral wire and keep it with each ornament for next year.
As you're adding your ornaments, work from the top down and take photos with your smartphone as you go so you can see the bare spots.
Put the large ornaments on first, then fill in around them with smaller ornaments. If you cluster your ornaments in groups of three with one large and two smaller, your composition looks more intentional.
Instead of a traditional tree skirt, we like to use a vintage linen sheet to wrap the base of the tree.