Some days there literally isn't the time to think through putting an outfit together. For me, those days are almost always Tuesdays. It's my running around day, when as well as whatever work I have to do, I have the school run (both ways) and Mini-Me's ballet class, during which I sometimes attempt to do some work, and sometimes just drink an enormous bucket of coffee.
On those days, I fall back on the things that are easy to throw on and always look good together: skinny jeans, my favourite worn-in men's shirt, a trench and a good pair of heels. Lately I've also taken to pinning a couple of loops of a pearl string together with a vintage brooch (as seen on Instagram) – it adds a bit of polish to the old reliables.