First, make sure you carefully read and follow the rules of the competition. Using dummies is fine if the rules of the competition allow it. Have a plan of how you are going to create and decorate your cake. I like to put my ideas and details on paper. Pay great attention to detail, even the smallest element of you cake is important. Work as neatly and cleanly as possible. If you add something to your cake and you are not happy with it, take the time to change it. I mentioned to have a plan before you start, but if in the process of decorating your cake you come up with something you think is better or will have more impact, don't be afraid to change it. Although I start with what I think is a good plan it often changes and most times I'm happy I made the change. When I enter a competition, I never expect to win, but I do expect to challenge myself. My first 2 competitions I took 2nd place in my class and the 3rd time was a charm! I won Grand Prize in the Divisional show. I was totally shocked! You want to do something original and creative with a difficulty factor to the best of your ability. Don't forget to pay attention to your cake board. It is an important piece of you entry. Neatness, Neatness, Neatness! Good luck and have fun with your entry!