The best way to learn any language is through immersion, either in the country or an Italian-only language camp. That said, if you have to choose between classroom instruction and audiotapes, you might be better off with the Pimsleur method. Contrary to the above claim, Pimsleur works on a recall and sentence constructions approach, which is based on studies of effective memorization and language acquisition: you are introduced to words through a graduated interval of recall, where you must use them often in different sentences early and then a few more times at further intervals in the training.

It is a truism that doing the first 30 Pimsleur lessons in a language teaches you everything you need to know to immerse yourself in it. You should have the rudiments of direction down, pleasantries of conversation, and most importantly, you will be absolutely fluent at saying: "Excuse me, I speak Italian but I don't speak it well. I didn't recognize that word, would you repeat it slowly please? Thank you!"

If you're doing a Pimsleur course, or studying from a person, the best thing you can do to supplement it is to immerse yourself in the sound of Italian. Listen to Italian radio on the Internet, watch Italian movies, find Italian kid's shows if you can. If there's an Italian-speaking meetup or cafe group in your city, attend!

Also, although this is better advice for French than Italian (which I do not understand or speak), if you're stuck for a word, think of the most high-tone English way of saying it, and 'Italianify' it. If you can't think of a word for 'strength', well, 'fortitudo' might get you laughed at but I bet they'd understand you.

Good luck!

Edit: Some people find Pimsleur easy, other's find it vexing and difficult. The difference is usually that Pimsleur really should be done one lesson a day. When I skip two days on Chinese, it sucks, so don't take breaks longer than one day and you should be in it within a month.