If you have one of those perfectly shaped fake trees, you should look for color-coded branches and put them in in the right order.
If you have a real tree, well, the fake tree stores might still be open...
Next, put in the lights. Lots of lights! Step back, squeeze your eyes a bit and look at the tree through your eyelashes.
This way you can check if the lights are distributed properly. Same goes for all the other decorations.
If you put candy in your tree, make sure you put it low enough so that the kids can reach it.
If you put it out of reach, they WILL find a way to get it. And most of the time it ends badly for the tree!