Schematcis with breadboard examples
From the sysrecon.com site:
Common Resistor values used with LEDs 3.3 volts to 5 volts: 330ohms 6 volts to 9 volts: 560ohms 12 volts to 15 volts: 1Kohms
http://circuitdigest.com/electronic-circuits/heart-shaped-serial-led-flasher
http://circuitdigest.com/electronic-circuits/fading-led