It's an old cliché which has been worn even on here Laconfir, but practice makes perfect. As you probably are aware, there are alot of similarities between French and English. And le français québécois has a lot of "franglais" in their dialect. It is still French though, which is where I have to disagree with figfarmer.
For example, in France you say être à la mode, in Québec être
in. The word "mec" isn't used nearly as often in Québec as it is in France. In Québec the word "chum" is very common. In France, you "faire des courses"; in Québec, you "magasiner" (to shop, to go shopping). I've been starting to see in La Presse (
http://www.cyberpresse.ca - an excellent place to start reading Québec French) the usage of the term "le week-end" instead of what Québécois usually say "la fin de la semaine".
Of course, going to courses etc is a fantastic way to start learning it. However, to complement that practice, read widely in French:
http://www.lemonde.fr or
http://fr.yahoo.com or even go to the Canadian Yahoo! page and click on the "Français" button. Immersion in French (which is the main method of French teacing in Québec) is the best way to quickly and easily learn it.
Generally, if I'm communicating in French, I use standard French and where I feel appropriate, I'll use
l'argot québécoise. I don't do that often because I don't know enough
argot to use it properly. All the Québécois can understand and perfectly communicate with you using standard French - I had one say to me "your accent is cute" when I spoke to her in standard French.
The Québécois accent, however, is very hard for a European French person to understand unless they are exposed to it on a regular basis. It's like a Canadian trying to fully understand a deep Scottish or nasal Australian accent. I've tried to master it whilst I was in France last year, but I never got anywhere near close, so I stuck to standard French and English. Many a situation I have noted whilst I was in France of a Québécois having to repeat himself three times for the European French to understand.