If you're invited to an event with a dress code, there are certain rules of etiquette that dictate how your dress should look:
A blazer dress code means you should dress up a bit more than usual, but not too formal. A knee-length or ankle-length dress in any pattern or colour is perfect.
A dark suit dress code is a bit more formal. Opt for a dress that falls below the knees in a fancier fabric like silk or velvet. Stick to more muted colours.
A tuxedo dress code is a chance to get glammed up. Choose a festive dress in silk, chiffon, or velvet. Just make sure it's not too long or sparkly, or you might be mistaken for a tailcoat dress.
A tailcoat dress code is the most formal, so you'll need an elegant long or evening dress. Think classic styles and luxurious fabrics.