What makes a good poster?

In my opinion, a good poster is something that grabs the attention of someone and makes them look at it and say "I want to go there" Or I want to do that. Whatever that poster is advertising when someone sees it they think that they want to go there or do that. It has to be absolutely wonderful. You have to make sure you are actually focusing on the project its self and not something that is close to the project. What I mean by this is if you have to make a travel poster for Cancun don't focus it on Hawaii. Make it eye catching and amazing. Make the customer say I want to go there or I want that. Make it so thats all that person thinks about it. but also make it fun.!