I think this is why the 50% rule is so important. What you are talking about is the drawing for fun part.

It looks like you might have drawn these digitally. If you have I would advise turning the opacity of your layer down to say 15-20% and add a new layer on top. Now re-draw what you have done using both your drawing and the original as references. This should provide you with an improved iteration of your drawing. Repeat if you like.

I often do this on paper and use a putty eraser to lighten my original drawing and then draw over it again to improve it.

What this will do will highlight the bits you are getting wrong and allow you to correct them. Over time you build up your sense of what is required ie relative size, negative space, angles etc. You will learn what is required, your line technique will improve etc. It is a very iterative process.

Generally your brain will learn by doing until eventually it just starts to know what you want. The more natural your ability becomes the better your drawings will be. It takes a lot of purposeful effort to achieve.

Do be careful with manga style drawing though. It is fun to do because you get results quickly but can be very flat and over-simplified and that can be limiting.