Here are some tips from the experts…
First, the lights. You will need 100 lights per foot of tree.
Secondly, those light strings contain lead. So wear plastic gloves to protect your hands, and wash your hands afterwards and before eating anything, so you don’t accidentally contaminate yourself.
Now for the decorating…
From what I’ve observed on YouTube, you can approach this a number of ways. Some people start by wrapping the trunk with a string of lights. Some people weave the lights up and down around the tree, and others wrap each individual branch, starting at the trunk and working outward.
Here are some videos that demonstrate those techniques…
Here’s the “wrap each branch” technique from Colonial Wiliamsburg…
And here’s the “weave around the tree” approach from Home Depot…
How do you put up your Christmas tree lights?
