Thanks for the comments. I will look into this.

By the way: I did not create any of this from a cylinder. I started with a simple box (cube) and shaped the head out of it. Then I extruded everything from this one.

The legs have some muscles in the lower leg and upper leg and the lower arm and upper arm is differently shaped. Maybe you cannot see this in the small image.

I think you are right with polygon flow. I could use more loops (e.g. in the stomach area) and more special shaped lines to define muscles.

But I am here at 3000 polies and I want to add bags and a headset. So I stopped it though I really would like to add muscles even to a female. I love that. But this time it will be better painted or will come later with the normal map that will be created from a way more dense model.

I did not understand your comment concerning uv-mapping. How do you know the use of it? I still do not use it because I have no textures applied so far. I finished the uv-map yesterday late night.
I did not use mirroring because it was a main point of critics in my last model here in this forum. The other reason is normalmapping. As far as I read in some articles it can lead to problems with normalmapping when you use mirrored uv-parts.
Some empty spaces in the uv-map are for purpose. I still have to map a few bags and a headset.