how to make characters more unique?

I would agree with playing around with shapes(be body type or their design pattern). It gives a more feel to a character instead of the body type or pattern looking one basic note.

Another tip is to experiment. Step out of your comfort zone a bit a draw or make something new to your pallet(Be making characters having a certain dress design you aren't familiar with, or work with a both light and dark colour pallet). To get a feel and dip your toe in something new or something you are not familiar with. 

agree with shapes, and try to mix the hairstyles in too! for example someone with long straight hair then someone with short curly hair and everything in between!

I always Focus on shapes before colours. And I keep my colours limited anyway. Shapes is what makes the character recognisable :). Experiment with different heights, body shapes, facial features, ethnicities if you’re making humans etc everytime you make a character. That’s why I avoid using things like bases. Reference things from real life as well! Including people, animals, maybe look at some professional character designers online as well for inspiration. 

Also I went to your page and noticed that you draw really simplicitic mouths, head shapes and noses, I used to do this to and I feel like this really held me back in terms of character creation, especially noses and headshapes. Using a variety of different shaped heads and noses can really make all the difference when it comes to designing characters.