Keep your topic narrow enough so
that you can finish it and do a good job on it.
Example:
"Plants" is a poor topic. You will not be able to learn everything about plants. Be specific. Pick a particular plant and choose one variable to test.
A better topic would be:
How does the distance from a fluorescent light source affect the growth rate of hydroponically grown ivy plants? How will varying the distance by 5cm in each group affect the growth of the leaves and roots?
State the purpose of your project
Example:
The purpose of this experiment is to find the best distance from a fluorescent light for growing ivy cuttings. We have been growing ivy cuttings in water on the windowsill for many years. Now, I would like to try to grow them under our new fluorescent light. My mother will be able to use my results to grow ivy cuttings for her friends.