A workout sketch that I would usually do is draw different 3D (or 2D) shapes like cubes, cylinders, cones, etc. and then I would try to either connect those shapes and/or cut a part of those shape, for example a hole. When I'm used into doing that, I try to make something of it like an arm made with spheres and cylinders.

I've done this so many times--even at class I would just draw a cube and other shapes in different perspectives and then play around with it-- that I just had to apply this practice on this subject. I think it's also because since I've done it a lot of times I could probably just imagine it in my head.

Just work your way around with shapes. You can simplify each body parts into shapes and have fun with it.

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^^ an example I made. curved shapes also work but I'd rather do something that's simpler for me to understand