To prepare for the scan, please do not eat (or eat very light) for four hours beforehand and be normally hydrated with water, tea, etc. Don’t over- or under-drink.
Also, do not do any heavy exercise (eg, a gym workout or long run) for the same period.
Please remove as much jewellery as you can before you arrive at the clinic. After you have checked in, empty your bladder before being called.
It’s best if you are in the same state for every scan for the most reliable comparison.