As far as I know, advertising on the forum works very well, as some forum users have already said.
As an adequate option, you can try to order leaflets and distribute them in large cities, it might work
As for the flyers, I wouldn't say it's a good idea. Certainly not in cities (or even countries) where advertising gambling is prohibited by law.
When it comes to advertising casinos on forum, I think it's a good idea. I think it would be quite interesting to create threads advertising the casino not only on Bitcointalk, but in all forums with gambling sections.