A successful project requires use of the "scientific method." That is not difficult; it only requires that the student: Observe, Plan, Experiment, and Explain what happens in the project.
Usually applied in a series of steps, the scientific method includes:
In order to form a generalized conclusion, an investigation must include a number of observations of the events being investigated. For example, if the question is "Does the presence of sunlight affect the growth of petunia plants?" then a dozen petunia plants must be examined over a time interval in the presence of sunlight (experimental group), while another dozen plants must be subjected to the same conditions but in the absence of sunlight (control group). Using one or two plants in each group will not produce a valid investigation.
Conducting the experiment