If you have no defined waist, your hips tend to have similar width as the shoulder, you do not have a lot of curves, your bust tends to be small or average and your bottom tends to be flat, it means that you have a rectangle body shape. This body shape is easier for dressing. Many models tend to have this body shape or the inverted triangle shape. Many clothes will usually suit you and fit you well.
Avoid to wear shapeless clothes. If you want to add curves, avoid straight dressed but you still can opt for the waist-less look. Use strong blocks of color to help define your body and be sure to wear a good bra to define what bust you have. Take a look at these 38 best way to dress for rectangle body shape below.