Steps
Purchase your nunchucks. Go to a quality martial arts site and get foam or rubber training ones with cord. Do not buy a set of wooden, metal or hard acrylic nunchucks for your first time around.
Purchase a book. Nunchaku; Karate Weapons of Self Defence is a helpful intermediate guide for individuals who are experienced in martial arts. However, you may want to invest in a book that is aimed at a beginner's level.
Do your research. Watch Bruce Lee's "Fist of Fury," paying close attention to the scene in the karate dojo. Play the video game "Soul Calibur" as Maxi. Go on YouTube and search for "nunchaku" and/or "nunchuck tricks". This is high level stuff and is not as hard as it looks.
Feel your nunchucks. they should be soft, not HARD like you might expect
Learn basic tricks. Now you have "the feel", you can spin them faster, do figure 8's, pass them under your legs, over your shoulder and under your arms.
Try the complex stuff. Try to replicate a few of the moves you've seen on the Internet. Naturally, take it slow for your first time around. Work your way up the ladder, as many of these complex tricks are simply basic techniques used in an unusual way. More often than not, then are all just basics executed with brilliant speed and impeccable timing. It can be difficult to remember to start off slow, but persevere and you will learn quickly.

Tips
Passing is relatively easy in that you swing the nunchucks so that the free end travels round your body or body parts, to be caught by the free hand. Use your imagination.
Once you are accomplished at passing, try to perfect a technique that allows you to curl the nunchuck around a body part without the free hand interfering. Essentially stopping the nunchuck swinging out of control, this is useful for practicing with two pairs of nunchucks.
Practice! You won't get any better without dedicating some time out of your day to practice tricks and maneuvers.
Look at actual martial artists perform with and without nunchucks, and get the idea how to use that for an impressive trick or two.
Try two pairs at once. See what you can do!
Progress onto rubber nunchucks (If you haven't yet) when you feel ready, as rubber is a heavier material, then move on to wood.
If you want to use a second pair, purchase one of the same type as the first, so they are the same weight, length and in balance.

Warnings
Be aware that, unless they are used properly, nunchucks can and will seriously injure others, if not possibly yourself. Take care when showing off your tricks.
Wooden, acrylic or steel nunchucks may be illegal in some states or countries. Check before buying.
As I said before, nunchucks are essentially ancient, deadly weapons. this article in no way gives you any right to go round the streets with a pair beating people up! Although using your 'chucks is fun, it is a tool of the martial arts and should be treated how you would treat any other weapon or martial art. With respect.
Be sensible. Don't try to do completely insane tricks you see someone like Maxi do on a video game. They are almost impossible and should not be attempted for fear of cracking your head open.

Things You'll Need
Foam or Rubber nunchucks.
A large space to practice.
A buddy present in case you knock yourself out!!
The commonsense not to show off - maintain self discipline