Step 1: Create Circuit
Here is a link to the Chibitronics how too so you could learn how to make a circuit of your own.
Step 2: Choose Effect
Chibitronics come with a variety of effect from a programmable arduino style chip to twinkle, pulse, fade, and even a light sensor.
I chose the light sensor and it works pretty well. The way it works is you add power to the sensor an create parallel path for the led and firmly press the copper tap on the leds to make the connection.
When the circuit is complete just place a copy of the design on top of the circuit and tap the ends together and clip on the battery and you are finished.