I also did one of those courses when I was 20 (are we more gullible then?)
I knew nothing about aviation then but had been a travel agent for a couple of years.
The course did give pointers on interviews, grooming and general behaviour
however...
I agree with exmax, you can probably learn at least as much from others here.
I've now been in aviation for 11 years and will also offer any assistance
Basically if you have no experience at all
Get experience of customer service, restaurant, hotel, travel agency, anything that gives you contact with the public
(Ticketing is always good as it helps your knowledge)
First aid training or nursing experience still goes down well
and languages always help (not always a requirement for interview these days - but invaluable in the job)
For the interview, dress smartly in a suit (skirt if female) try and wear a similar style / colour to the company, it helps them see you in the uniform
Make up should be subtle and colours that compliment the uniform can help
Always be aware of your actions, whether in a formal or informal area, I've heard of one person not getting the job because they carelessly let a door slam in someone's face when leaving a room!
Anything else don't hesitate to ask