I love quick and easy ways to make an outfit special, different or fun. I can't take credit for this trick (I read it in a magazine at some point). However, I employed this trick during my teen years in the 80s. Back then I used my denim jacket and concert buttons but it's the same idea.
Just take a few different pins and cluster them on the shoulder of your cardigan or the lapel of your jacket.
Isn't that simple? The beauty is that you don't even have to give thought to the size or color. It's brainless. Mismatching is the key. That's what makes it interesting. If you'd like to try this and don't have any pins or brooches, you can pick some up at the thrift or vintage store. I love the grab bins where you can get them for $1. Mix it up, to your hearts content.