Step 1: Materials
Wire (2 colors)
Meter stick or yard stick
Knife (a flat carving knife works well)
Battery pack for arduino (helpful but not required)
Step 2: Prepare your LED's
Even if you don't have clear LED's, you might want to bend your wires out a little so you don't accidentally solder them together.
Put some solder on each lead. This helps a lot later.
Step 3: Prepare your wires
Stretch out both wires on your working surface next to your meter stick or yard stick. Tape the ends down so the wires stay straight.
Now, decide how far apart you want your LED's to be. Use your knife to cut a notch in the plastic insulation at each interval.
Put some solder into each notch. most of the solder should be sucked into the wire.
Step 4: Put it together
Just heat it up!
Hold an LED so the lead is touching the bare wire in the notch. Make sure that the short lead is on the ground wire and the long lead is on the other wire. Use the soldering iron to melt the solder on the LED and wire. Some of the solder that was sucked into the wire should come back out onto the lead, which helps strengthen the bond.
Repeat for each LED on both wires. You should end up with a string of LED's somewhat like the one in the second picture, but not wavy. I bent the wires to test the string in a project that I am working on, then unbent them for the picture.