Research your topic. Gather information regarding your topic on the Internet or at your local library. A strong hypothesis must always be a well-informed one.
Cite evidence regarding similar experiments. Examine the findings of professional or graduate-level research. Defend your hypothesis using the most common results in those experiments and explain why they're likely to be repeated in your experiment.
Explore both the dependent and independent variable(s) to be used in the experiment. The dependent variable is consistent throughout the experiment, while the independent variable changes. Your hypothesis should be based on the likely effects the independent variable are to have on the dependent variable.
Perform the experiment. Closely document all steps and findings throughout. The best way to back up your hypothesis is to prove you were correct.