I wish I was an expert on dressing for cocktail parties or interviews, but I'm best at choosing attire for medical appointments. Doctor visits, diagnostic tests, physical therapy, etc I'm on it. For example if you're meeting a doctor for the first time you want to look nice from the neck up (esp if people think you're several years younger than you really are). From the neck down you want clothes that allow him to observe your movement and examine you without having to strip and put on a gown big enough for a refugee family to live in.
Generally, no metal is a good plan. Ortho's often take X-rays in their office. Also, it's just more comfortable to lay on a table without bra hooks digging into your back, etc. If you're comfy in your clothes you'll be more receptive to stressful information. I know I am. Also, wear your walking shoes.
That's all doctors where donning the gown is avoidable. When you can't get out of it like at the Gyno there are other things to think about. Easiest clothes to get in and out of and slip on shoes. I've starting wearing a comfy dress and then if you only have to disrobe waist down you're still covered. You stay warmer and you don't have to wait with the paper sheet across your lap.
When going for a test/lab work I still say go comfortable, metal free and wear your walking shoes. Don't bother with hair and make-up it's pointless, trust me. Also, consider what is absolutely necessary to bring (id, insurance card, keys, etc) and pick pants with pockets. It's so awkward juggling a purse, finding a place to set it down and so on. Just bring the essentials. I do say pants here because it's always freezing.
I don't know if anyone else deals with these things enough to care, but it occurred to me that after nearly 30yrs I have a pretty good grip on it. Too bad "dressing for an MRI" isn't appropriate for the skills section of the resume.