There are many ways to "improve" your designs, but I'll give you this little guide rule (don't follow it step by step as some sort of manual):
1. Where and why does your character appear. Think of this as the context, is your character from a medieval period or from the modern era, is it rich, or is it poor? Think of general qualities that may influence your characters looks.
2. How does it wants to appear. This is pretty much self-image, what its meant to portray, is it shy? brave? cool looking? On this point I like to idealize and exagerate my characeter concept to make a base, I keep it really simple since there's more you can add to it.
3. How does it actually appears to others. This is hard, but you pretty much want to take what you made on the previous point, and break it. Quite literally, think of it as mixing both of the previous points, and make and accurate representation of your character's self-concept and its context.
4. Take a break, looks for some inspiration, work on your design mentally, and come back to your design. Sometimes we miss a few odd things on the first go, and only after a while we realize "something's wrong". As from experience, sometimes I work on a character for weeks just to give a it complete redesign after a month.
5. Share. Its fine if you don't want people to watch your work for whatever reason, but trust me that getting feedback or just a mere impression from others is so valuable when designing a character, for example if you talk to someone with more experience you might get some good tips, on the other hand, if you get into a non-artist person just a little "looks cute/cool/evil/kind" type of reaction can tell you that your character might or not represent what you wanted.
Hope these little tips can help you!
