Avoid: Jeans, minidresses, wild prints, or "club like" clothes. This is generally not the occasion for your cutout crop top.
Instead try: A floor-length or ankle-skimming gown. A really nice pair of pants or well-tailored pantsuit is a great option too, especially when completed with a fancy top. While some cocktail-length designs can be appropriate at times, they shouldn't be too revealing or lack in sophistication, and you'll see far fewer than you will long dresses. Men should wear tuxedos or dinner jackets, and bow-ties are a great add-on. Don't be afraid to reach out to friends and family who are also attending the event to compare notes. If the location is glamorous, then sure, reach for the sequins.
Image Source: POPSUGAR Photography / Matthew Kelly