The first step in this project is stating what you are going to do, namely growing a plant using tap water and sugar water and then gathering basic information on your materials and plant growth to make a hypothesis. Your hypothesis states what impact you think sugar and tap water will have on the plant's ability to grow. For example, your hypothesis might state: "Plants grow better with the nutrients of sugar in the water." The project will require running experiments to prove your hypothesis right or wrong, compiling your data and then showing the results at the science fair.
Plant growth with sugar water versus tap water has the experiment built in to the title: growing plants. This experiment requires you to grow two plants in nearly identical conditions as this will yield controlled results. The only difference between the two plants is the type of water each is fed. All other conditions must be the same including the plant type, pot size, soil type, light and the amount of water given to each plant. It's important to note that this is not the kind of experiment that can be conducted at the last minute. Ample time is required to grow and observe your plants. Additional time is necessary to plan for the unexpected, such as your dog eating one of your plants.
Without careful documentation, even the most important scientific discoveries would be unknown to the world. For this reason, your science experiment requires careful note taking on details such as daily water amount and growth progress are crucial to the success of your project. You only need a pen and paper to accomplish this, but you can score additional points with other types of media such as pictures or video. An ideal documentation strategy is to create a blog or website with regular updates on the experiment and process you take. Not only does good documentation increase the quality of your project, it also helps make the final part of the process -- reporting and presenting -- easier to complete.
As your plants grow, take pictures, record notes, make measurements of plant leaves and stem height and observe the overall health and quality of the plants. This type of data is recorded in a report, which includes your reflections on how your hypothesis was proven or disproved. The report explains all of this in a clear and straightforward manner and is also the basis for your presentation. At a science fair, you want to be able to convey the process and results in a conversational manner, providing the entire story in a few minutes. You'll also have materials to display such as the plants or pictures of the final results.