Mistake 1: Making Connections Outside Electrical Boxes
Never connect wires outside of electrical boxes. Junction boxes (or a J box) protect the connections from accidental damage and contain sparks and heat from a loose connection or short circuit.
Solution: Add a box
Where connections aren't contained in an electrical box, install a box and reconnect the wires inside it. The photo shows one way to do this for an exterior light mounted on wood siding. While you're out there, consider upgrading your outdoor security lights, too.
Mistake 2: Cutting Wires Too Short
Wires that are cut too short make wire connections difficult and—since you're more likely to make poor connections—dangerous. Leave the wires long enough to protrude at least 3 in. from the box.
Solution: Extend wires
If you run into short wires, there's an easy fix. Simply add 6-in. extensions onto the existing wires. The photo shows a type of wire connector that's easier to install in tight spots. You'll find these in hardware stores and home centers. Learn how to properly prep wire.