The key to keeping this look a step above your typical "jeans and t-shirt" look is all about the pieces you put together. Think "slim" not "sloppy" and "polished" but not "perfect". A dark denim short keeps this look from entering into a very casual territory- no rips or fading here. The top half is fitted, but not tight. Pairing flip flops or sneakers is totally okay, but stay away from rubber flip-flops or running shoes; save those items for the beach and gym. Feel free to accessorize, but keep it light. Pile on some skinny bangles or rope bracelets.
I can't help but grin thinking about how easy it can be to look chic in just jeans and a t-shirt. Yup. Pretty great. Don't you agree?