Bulbs

• Those tiny glass bulbs that emit light can cause more trouble than all your other Christmas decorations combined. Before trimming your prelit tree, plug the lights in and stand several feet back from the tree. If you see blank spots where lights should be twinkling but aren't, start by tightening the bulbs in these areas. If this doesn't work, you need to replace the bulbs. Most prelit trees and additional strands of lights come with a few such replacement bulbs. If you've used up your supply, they are easy to purchase in almost any store that sells Christmas decorations.
  
  

Wires

• Carefully inspect all the wires on the strings of lights on your prelit tree while it is unplugged. Damage can occur during storage, and it's important to find out whether that's the case early on. As you inspect the wires, look for bites (small animals sometimes infiltrate even the most secure attics and basements) or areas where the wires have worn. If there is any wear on the wires but the inner wire is still intact, completely cover the area with electrical tape. This will prevent sparks from coming from the wires and onto surfaces that could potentially start a fire.
  
  

Fuses

• All strings of Christmas tree lights have fuses in them. When these fuses blow, the lights will simply stop working. Whenever an entire strand (or in this case the entire tree) ceases to light, check the fuse before you try tightening or replacing 100-plus tiny light bulbs. Almost all of these sets include additional fuses, but you can also purchase them at stores that sell Christmas decorations as well as most home and garden or hardware stores.