Disclaimer:
You have the right and freedom to wear whatever you want for your headshots. The info below strictly opinion based. At the very least, it can help you ask yourself the proper questions in order to make apparel decisions.
Clothing:
Solid colors work best. If your favorite shirt that gives you an added layer of confidence happens to be a pattern, stick to bigger and/or non-busy patterns. Any tight pattern will be very distracting and take the attention off of your face. Secondly, consider what you want your end-user (client, recruiter, hiring manager, etc.) to see and feel when they look at your headshot. If you're an actor who specializes in rom-cons, then a bright color shirt can give your headshot a boost of energy. If your a lawyer who wants your headshot to give a "no monkey business" type feel, then stick to traditional white, light blue or gray solid colors.
Jewlery:
Again, think of your end user. If you're a social media manger for an "edgy" company/client, then big earings and facial piercings may be the feel that you're going for. If you're applying for jobs in the coorperate world, even in the tech strartup realm, I'd suggest to keep it simple. No facial jewlrey (small studs if you can't take them out) and keep the earlings and necklaces on the smaller and elegant side. They should be an accessory, not an attention grabber.
Jacket/Sport Coat: For either Men or Women, think about the job or clients that will see your photo. If you feel your customers or hiring manager would feel more comfortable with someone who acts with 100% professionalism (straight to business, no small talk) then a suit or sport coat may be the best bet. Since headshots are generally elbows or shoulders and higher, no need to wear the full suit. Just bring the jacket to the session and put it on right before we shoot. Don't wear it while driving, it will wrinkle! If you want to appear more friendly and approachable, then I'd skid the jacket. A nice and professional top (longsleeve button down for men) looks great in headshots and gives the end-user the feeling that you're easy to talk to.
Tattoos: There's a theme to all of these categories and tattoos are no different. Just ask yourself, "would my future client or manager care if I had visable tattoos?" If your tattoos are unable to be covered (mainly neck and facial tattoos), I can photoshop them out. However, keep in mind that this can be percieved as misleading to your client or hiring manager when they end up meeting you in person and see said tattoo. Sometimes people are in the process of having them removed and it would be gone by the time they met anyone. It's a $25 additional charge for this service as it is a difficult process to remove them and make it look natural.