The key to good 3D is good 2D. Once the curves have been well thought out and created the sculpting process can start. It's like aircraft construction which includes the basic frame construction then applying the outer skin. Image 1 shows us the body frames, and Image 2 shows us the outer surface. The previous examples exhibit a good model build upon these principles. All the features consist of good curvature. Having a foundation on the drafting board with the understanding of blueprints, linear perspective, and isometric mathematical drawings built a strong foundation in 3D. If you can't envision the design in your mind the end project will never be good.