What Joy said! This was tough for me to figure out too (and still is) but Angie's ensemble suggestions help to simplify the process. Today's outfit is an easy one. I'm not claiming it's a brilliantly creative outfit or anything,; it's copied directly from Friday's blog post! But it definitely incorporates juxtaposition and trying that in a failsafe way gives me the confidence to attempt my own versions. In this case there is casual (a sweatshirt, jeans) combined with polish (the sweatshirt has sequins, the jeans are white, the boots are pointy toed and highly polished). The jeans are structured, the sweatshirt is soft. There's also a subtle pattern mix because the belt is leopard print and the sweatshirt is houndstooth (but tone on tone, so not terribly visible.)
Many times when outfits don't work it's because of a proportion issue. This is especially true when you are playing with items from different capsules in your wardrobe (i.e. dressy with casual). So it does take some experimentation.