I think your sketches are great!!
As the other guy already said, i'd recommend you to use photos for reference. See it as a way of training yourself about anatomy, proportions, some intuitive perspective and even a little bit of technique if you are willing to try.
Copying from photos is great. You dont need to copy a pose and then draw on top, what you should do is to copy hundreds and thousands of different poses and body features. Thing is you cannot draw something you dont know, and to get to know the human anatomy, you have to see it, and reproduce it over and over. It will be recorded in your mind and in your muscular memory. Once your brain comprehends the volumes and overall rules of the human body, and your hands know what the hell is needed to draw those lines, you'll be one step closer to be a great artist. Of course, if you manage to get live models, better.
As for technique, you can also experiment on your own but i'd recommend tutorials, videos or actually tutors, since the technical part is always a set of rules to get the hang of more than something of expression and meaning. Read about different materials, color theory, perspective, layouts, etc.
The last part is the artistic part, your sensibility. If you wish to be a designer, i guess there's no need to invest that much time in this department since your job would be design with functionality in mind. You do a character like this or that and thats it. Otherwise if you wish to go to the more artistic meaningful path you need to study. Study art history, study artists, read and read more until you get it. This is the part where you learn without touching a pencil, its entirely inside your head, you have to develop your artistic sensibility, and there is no right and wrong. Is the most subjective part, you can be either acclaimed or rejected, regardless if people actually gets your message and the meaning behind your work and expression. And of course this is the kind of art that will make you feel more rewarded, since ,supposedly, you wont be doing it for money or for commercial purposes. You would be making actual art. And art, for me, is the exploration of the very nature of mankind and the exploration of the meaning of life itself. I believe that anything you make art from is linked to this ideas, one way or another.