I am certainly a fan of this trend, however I'm not a fan of those that style it incorrectly! In my opinion, there are a few ways in which sweaters and jumpers can be styled in a casual way for wear with an outfit.
Firstly, paired over jeans or pants. This is the most common way of styling, and it is also the most easiest and relaxed way to wear the trend. Make sure you're styling your shirt or sweater with a pair of pants that either match, or complement the outfit. What we don't want is the combination of a fluro shirt with a pair of denim jeans- thats a no no. Simplicity and a matching look is key. Plaid and tartan patterns look great when tied around a pair of jeans- as they compliment each other. Add a white tee on top with a leather jacket and you will look incredible.
Alternatively, you could try styling the trend with a skirt or a dress. This look is a little tricky to pull off but the aim here is quality over quantity. The main attraction should be the sweater/jumper, so make sure that if its coloured or features a pattern; that is paired over a neutral style skirt or dress. If you're wanting to pair it over a skirt- try a skort which will make the look quite eye-catching with the combination of shapes. If you're pairing with a dress then wear with either a bodycon or t-shirt dress. Denim shirts with a white or striped dress look best.
Thank you so much for your question and I hope this has helped you! Enjoy the inspo pics.