What I did (for med) is make a big list of all the skills/qualities that I thought made a good doctor, then thought of examples of where I've shown each one. I prioritised writing about any actitivies/experiences that cropped up for multiple skills, e.g. being football captain shows leadership, teamwork, communication skills, so would be better to write about that than, say, how crocheting improved my manual dexterity. I would also be very careful about sending your PS to others - there is a risk of plagiarism if you post it/send it to someone online. You might be better off asking teachers, friends and family or anyone you know that is a dentist to read it through. Hope this helps!