Cardigans are a spectacular building block for an outfit. They're useful as a classy touch for a more formal outfit on a cold day over a dress shirt and tie, since the buttons add a wonderful element of class missing from the traditional sweater. In addition, a bulkier cardigan as outerwear is incredibly useful if you want to add an element of contrast to your silhouette, paired with more slim fitting pants and a closer fitting shirt.
Shorts were very hard for me to come to terms with. Cargo shorts are hideous, there is no two ways about that. Recently however, I've been experimenting with more slim fitting and dressy shorts, and it makes them much more workable. At or shortly above the knee, paired with, again, a nice dress shirt and slim fitting cardigan. They can look really elegant without being ostentatious, and can be really great in many ways. Also, a friend of mine has been cutting off skinny jeans shortly below the knee and cuffing them so they aren't all scruffy and they look great, far better than I ever realized denim shorts could look.