Humans are always a tough subject and I am no expert. I think the reason they are hard is we see them close to 24/7 so we recognize all our drawing flaws (and its natural not to like our own artwork lol). I don’t know what you need tip on specificly so it general on coming up. (feel free to note me or reply if nothing make sense ) ok no robot tips...
Have you tried tracing or copying from a photo/other drawing? It will help with proportions, shading, and muscle memory. I know it sounds weird but it has helped me especially when it came to horses. It helped me get everything in the right spot and helped me shade better overall.
Do white on black. Do you have black paper and a white pencil-crayon or white charcoal? It is weird (and good) to draw the light instead of the shadow. It will also help understand shadows/shading in a fun way (and always looks awesome )
Hope this helps! But if it doesn’t, put gears and wires on them then you have a steampunk twist and everything you draw
Well I use different techniques depending on the subject. Like when doing background hazy mountains, I use a tortilion to achieve the effect. But mainly I use layers.
Example: when doing humans (or anything light i.e. the color of the paper) I start by putting down a light base layer in the shadows then gradually getting darker and darker as needed.
When I am doing animals/darker subjects I lay down a medium layer in the shadows then go over the entire subject with a light to med base coat then darken or lighten as needed. Sometimes when doing this method, I need to go over the joining areas and add a light layer to smooth the transition from shadows to light.
When I draw I use a mechanical pencil and use the lead at an angle to give me a soft even coloring when used on its side and the sharp point created by that to do detail. (using a regular pencil works too I just find it gives rougher texture when used and might need a tortilion)
Using a tortilion (or your fingers) tend to blend the shading together and if you have been using that method that could be the reason. With using that i would recommend defined layers with no blending by pencil (i.e. dark to lighter with little in the middle) so that when you apply the smudging it blends