1.  Start by lighting the candle using the lighter or a match. If you used a match, blow that match out.
2. Blow out the candle.
3. Spark the lighter or light another match and place the flame in the smoke.
4. You will see the flame travel down the smoke and relight the wick.

How does it work?

To understand how the relighting of the candle via smoke works, you need to comprehend how the candle and fire each work.

First, fire needs three things to burn: oxygen, a fuel source, and ignition.  In the instance of a candle, there is oxygen in the air that we breathe, the paraffin wax (in the case of most candles) acts as the fuel source, and you supply the ignition by lighting the candle with a lighter or match.

When fire burns, you can tell the efficiency of the flame by the smoke produced.  A fire that produces a lot of smoke is an inefficient flame, meaning that it does not consume all of the fuel as it burns.  A truly efficient fire would consume all of its fuel and have no smoke. 

So when you blow out the candle in this experiment, you see smoke.  The smoke from a blown out candle consists of vaporized wax.  This gaseous wax is left over from the inefficient flame.  When you add a flame from a lighter or a match, you again have the three necessary parts of fire.  The oxygen is again in the air, the fuel is in the visible wax vapor (smoke), and the ignition comes from your lighter or match.

Additional Info

You can take this experiment further by trying out different types of candles.  While most candles are made out of paraffin, you can also find candles made of stearin, beeswax, or gelatins.  Also, there are scented and unscented candles. Since these candles are all different, they are comprised of different ingredients.  Try to find out which type of candle works the best with this experiment.  Does the scented candle's smoke follow its nose to relight the wick?  Does the soft gelatin fail to relight?