For those casual yet still tie-required dinners, maintain a mellow vibe by pairing a light-colored (and lightweight) sport coat with an untucked and slightly rumpled shirt. And always choose a solid tie that’s darker than the shirt and that’s in the same color family as the rest of your look (i.e., all blues, khakis, or grays). Forgo the usual cotton trousers and upgrade to a pair of relaxed-fitting white denim — and to roll up the cuffs, so long as you’re not wearing socks.

Cotton sport coat by Burberry London (sold as suit), $1,295, at burberry.com. Striped shirt by Band of Outsiders, $250, at Barneys. Navy cotton tie by John Varvatos, $125, at johnvarvatos.com. Vintage slim-fit jean, $98, and cotton braided belt, $40, both by J.Crew, jcrew.com.