I personally don't like the spray bottle method of training cats. I have found that postive reinforcement worked best for me. When I see them use their post instead of the couch, I give them a glowing "good boy".

Like Catmandu said, a stern "No" works well too - when they are trying to eat soemthing they sholdn;t, when they are jumping somewhere they shouldn't etc, a No in a deep voice and said sharply works... saying no in a whiny or indecisive way doesn't work. It has to be authorative. I also like "ut-uh". Most of the time, I give them the "Ut" part of "ut-uh" and they look at me and walk away from whatever bad thing they were planning on doing.