The traditional Rectangle is blessed with complete body balance so you can pretty much wear whatever you want.
The only challenge I ever hear from clients with this shape is that they want to add to add curves to their silhouette.
Here are my top tips:
Peplum detailing gives you hips.
Choose lighter coloured dress and jeans.
Horizontal shapes are great for adding the illusion of curves.
Higher necked tops and dresses conceal a modest bust.
A-line and flared skirts and shorts add width, as do printed and detailed trousers.
Trench coats and any jacket cinched are great for adding waists.