Oy, those are nicely exercices. Looks like you are building the observations skills very well.
For character creation... there's a LOT to be said. Many videos cover guidelines, tips and visual cues. I recommend just diving and taking a look at different videos and blogs by searching "art character creation"
From my own experience I can highlight a few points:
1) Keep in mind the medium. If it's for a medium like manga or animation where you need to redraw the same character many times, make sure to keep the design simple. If it's just for art, you can usually go crazy. If it's for game development, it's a whole different topic, like visibility, colors, etc.
2) Define the character archtype and main personality traits. Try to brainstorm what words define your character. This will help create the visual story.
3) Try to make the outline unique so it's easily identifiable. This doesn't just include the line itself, but a specific pose, physical characteristics. You can usually identify this by simplifying your character to a few lines (draw it in 1 minutes) and making sure it's still identifiable with a few rough lines.
4) This applies to much more than character design, but, don't be afraid to screw up. Create a design, then try to iterate it. Get feedback, iterate again. Leave it, try to do a new one aiming to do it better. Iteration and practice makes perfect. NO ONE gets it right the first time.
There's quite a bit more to keep in mind, such as style, consistency, color theme, and so on, but this is what comes to mind at the moment.
