Different ways for the preparation of the "Heure Verte" the "Green Hour" exist. Check out the following videos explaining how Absinthe is (and is not) properly prepared.
French Absinthe Ritual
The French Ritual is comparable with the preparation of Pastis Pernod or Ricard, the follower or substitute of Absinthe after its prohibition. You put one or two sugar cubes on an Absinthe spoon, place it over the glass and fill it with an amount of Absinthe (2 to 4 cl, about a tenth pint). Then gently water is poured over the spoon. The green Absinthe begins to louche into white sage. In former times so called "Absinthe Fontaines", "Brouille Sets" and "Reservoir Glasses" were widely used to dissolve the sugar with a thin beam of water which creates the perfect Louche.
Bohemian Absinthe Ritual
(..and why you should avoid it)
Meanwhile, the Bohemian (Czech) Ritual of drinking Absinthe has
become very popular. You put one or two sugar cubes on an Absinthe spoon
and pour Absinthe over it. Then you light up the sugar and wait until
the flames caramelize it. The sugar drips into the glass and blends with
the Green Fairy. Then water is added to create the Louche. We do not
recommend this ritual. The fine taste of the Absinthe is negatively
effected by the caramelization of the sugar and the whole preparation
can end in an disaster...
Brouille Absinthe Ritual
A Brouille is a small glass lid, which you place over your
Absinthe glass. It is then filled with ice cubes and you slowly pour
water in it. The water gets cooled and flows through a small hole in the
bottom of the Brouille into the Absinthe glass. The Brouille is very
easy to use and you get one of the best cloudy louches, because of the
extremly thin beam of water.
Fountain Absinthe Ritual
An Absinthe Fountain is an authentic Absinthe accessory which was present in every Absinthe bsitro during the time of the Belle Epoque. Out of the spigots water drips on the Absinthe sugar, dissolves it and blends with the Green Fairy to create the perfect louche.
Brouilleur "Auto Verseurs" Absinthe Ritual
Instead of an Absinthe fountain you can also use an Absinthe Brouilleur. The water flows over a see saw into the Absinthe while you listen to the mechanical "tic tac" sound of this Absinthe accessory.
Bouilleur "Two Level" Absinthe Ritual
The "Two Level" Brouilleur is like the "Auto Verseurs" an authentic Absinthe accessory especially made for the tech-fascinated Absintheur.
Brouilleur "Streamline" Absinthe Ritual
The "Streamline" Brouilleur is for the "inside out" Absinthe preparation. First you have to fill the glass with water and then you fill in the Absinthe using the little cup of the Absinthe Brouilleur, which injects a shot of Absinthe into the water and creates a swirly louche.
Interesting Info: Ernest Hemingway usually prefered a variation with champagne instead of water. There is an infinite variety of Absinthe cocktails, the first historically reported cocktail (the so called Sazerac) was an Absinthe cocktail.