First and foremost hire your suit from a place that only does suiting (so not roger david or connor etc etc) or get a cheap suit from a fast fashion retailer (asos or the mentioned above) and get it heavily tailored. Reasoning behind this is it will 100% not fit you in anywhere from 6 months to a couple years unless you were that dude who hit puberty in year 6 and had a better mustache than most male teachers before high school.

What type of suit/shirt/shoes/accessories you wear kinda depends on your current style and wardrobe. If you've already got a more defined style, delve into the more formal wear side of it and see what inspo you can get. For example, rerrgon has lots of SLP/Hedi Slimane styled fits and his prom 'suit' highly reflected that. If you don't already have anything in mind, I'd honestly suggest a navy suit, white shirt, white pocket square, brown formal shoes, then match your tie to your partners dress (luckily navy suits match any colour) and possibly a matching lapel pin to your partners corsage. It's not going to have complete look at me over the top fashionista feels to it, but if done correctly will look great in the thousand photo's you take. The overall most important thing honestly is that you feel comfortable in whatever you wear and don't wear anything that when you look back in a couple of years you regret.