For most people, following an outfit formula is the best, and easiest, way to look put together with minimal effort. My outfit formula is a lot of black (duh), and usually oversized pieces, with a mis of relaxed and tailored fits, as well as different textiles and textures, usually reserved for autumn and winter wear.
During the summer, getting dressed isn’t always fun, because it seems that no matter what you wear, you’re probably just going to sweat through it and feel gross. This is why I generally stick to a denim shorts and some sort of breezy top combo when it’s boiling hot out. It usually makes for a wicked tan line from my shorts, but I have managed to skip that this year, because of all the pool/beach days I’ve committed to.