Next week I plan to draw several cars by the reference and one of my own design.

That is a great way to study my friend.

For finding sexy shapes or sexy combination of shapes try to focus on contrast. Usually contrast of sizes, orientation or direction of shapes. Sometimes less is more. Also try first to focus on big shapes, or what conforms the silhouette, later you can deal with details and how those smaller shapes are being influenced by the big shapes. Other thing that makes shapes more attractive and dynamic is if you skew them or even if you just use a heavy perspective on them.