Adding a cardigan to a basic outfit such as jeans and a tank top will make the look so much more interesting.
If the tank top is relatively plain, either a neutral or a plain block colour, try adding a patterned cardigan. You can get brightly coloured cardigans with bold patterns or try a darker colour with lots of geometric shapes and Aztec looking patterns.
Try adding an oversized cardigan to a simple outfit such as shorts and a tank top to add interest and dynamics. This will also allow your summer shorts and tanks to transition to Autumn (Fall). I recommend sticking to plain simple style for this look but selecting a bright, vibrant colour to make the cardigan the focal point of your outfit.
I really hope you give these two ideas a try. Have Fun
Emma