Speaking from experience, I would say the 3 fundamentals of a good advertising is "WHAT", "WHY", "HOW". You have to state WHAT is your message, or WHAT product you are offering. Then WHY you are offering it, what are the reasons for your offer and then HOW it is going to benefit the consumers. These are three things you need to consider for a good advertising, i believe in my opinion. I am only an advertising student so I believe a person in the industry should know better than I do