The scientific method starts when you ask a question about something that you observe: How, What, When, Who, Which, Why, or Where? For a science fair project, your question should typically be something you can measure, preferably with a number, and should be something that is interesting and important to you.
What is the question your science project is trying to answer? Make sure that the question is testable, which means it can be answered with an experiment, and that it includes both the independent variable (IV or what you will change) and the dependent variable (DV or what you will measure) in the question. If you need to review variables, check out What Are Variables?
“How does __________ (IV) affect __________ (DV)?”
If you are using a Science Buddies project, you can use the Objective and Experimental Procedure sections to help you determine your project question.