What should I do to prepare myself for EEG study?

Nothing to do. there is no need to prepare for an EEG. Don't take any medications that you don't normally take.
Ask the facility. Most outpatient EEGs request that you are sleep deprived beforehand. Usually that means that they want you to get no more than 4 hours of sleep the night before. Apart from hair washing without conditioner beforehand there are not many other recommendations. However, if additional questions exist I would call the facility where you will be having it done and ask them.