The easiest way to dress up an otherwise simple outfit is to throw on a blazer. Nothing is as transformative to jeans and a tee, or as wearable in nearly any situation. The shiny lapels and loose, comfortable fit of this one has made it my go-to as of late. You can't go wrong with Elizabeth & James.
Céline sunglasses, Elizabeth & James blazer (similar), J. Crew tee and necklace (similar), 7FAM jeans (similar), Sam Edelman loafers (similar).