In terms of sketching out organic forms, I find it helpful to use underlays with all of the contour and joining lines first to work out the actual surface, and then use the contour lines on the underlay as marker guides for the shadows and highlights on the later sketches. I also find it helpful to trace over existing images that have the shapes/shadows/highlights I’m looking for if I really can’t get my head around it.
Start simple with a sphere, and then two spheres with a bridge between them and so on.
Two designers that come to mind for organic form inspiration are Luigi Colani and Ross Lovegrove. I did a Luigi Colani inspired speaker project when I was a student that definitely improved how I thought about complex surfaces knitting together.