Start thinking about your science topic right away. This will give you time to research and end up with a better result. The topic chosen should be one that is interesting to you, one that will keep you motivated. Search magazines, go to science fairs, watch television news or read newspapers to find ideas for your project. As you think of questions you have on a topic, write them down so you won't forget them.
Have a plan. Follow that plan step by step through the entire process, and don't rush through it. Just performing an experiment doesn't teach you how or why it worked; that takes doing research and seeing final results. Make sure you ask many questions about what you are doing and the processes you will be following. Keep in mind what you are asking about the project to help you stay on track and so that you will be able to reach a final conclusion.
When you begin an experiment it can seem overwhelming, but stay calm and pay attention to the steps involved. If you are working with someone, decide who will be doing each step in advance so that there are no mistakes and nothing is overlooked. Make sure you make notes, take pictures or record your observations during the experiment; for longer projects you should make a daily log. Don't worry if something takes a little longer than planned or if you are forced to repeat something. Experiments take time.
As your experiment moves along you may discover things you had not expected. Make note of these revelations, as they are part of the experiment's results. Don't worry if your experiment doesn't work either. It just gives you another learning experience. Ask yourself what went wrong and what is needed to change it. Many scientific failures turned into new discoveries, like the glue used for Post-It Notes.