Once you have some ideas, talk with your parents, friends and teachers. Scientists have a mechanism called peer review where colleagues ask questions about each other's work and give advice about what further experiments to try. The entire process I have just described is an embodiment of the scientific method. The gist is that the researcher should question their understanding of something, design and perform experiments to study it, and use that data to better explain it. As you perform experiments, write down enough information so that you are able to recall exactly what you did .
Scientists keep notebooks that summarize their experiments.
This is because experiments become complicated very quickly and it is important to keep a record of each step. Your notes from book research and your experimental design ideas are as important as the experimental procedures and the data from those experiments. These can be kept in the same notebook or in a different one. If you keep your notebook on the computer, make sure that you save it often and have a backup copy. Once you have collected some data, it's time to analyze it.