FOR WORK: you can layer over a blouse and trousers. If the trousers are a wide leg, you want to stick with a shorter cardigan. If the pants are lower and slim around the waist you can wear a longer cardigan and then belt it at the waist if you like. This will expand your closet by 3-5 outfits immediately.
FOR PLAY: pulling a cardigan over a simple dress will add a little "flavor" to the outfit. You can also pair it with jeans and a casual shirt for a more bohemian look. Don't forget to add jewelry or pin a brooch on the sweater for an old-fashioned look. Really the ideas are endless just try.
Add a belt - One way to give a cardigan more structure is to add an interesting belt. This can be an excellent way for a petite person to show off a tiny waist.
Button or unbotton?? - If you button it all the way, you can add an interesting belt or a scarf to complete the look. For a more casual look leave it open and add some interesting jewelry at the neck line.