What was the result of the experiment?
Keep clear, precise records (need I add "in your notebook"?).
Do your experiment again to check your results.
Have you eliminated all variables (conditions which could affect your answer but for which you are not testing) ?
Do your experiment twice to ensure accuracy.

When at all possible, illustrations of data are advisable. They create a professional appearance and convey a great deal of information. Examples include: Bar Graph, Pie Chart, X & Y axis Graph, Histogram, etc.