[Keal Atis] Learning to draw sprites

Hello, I have been following this forum section for a long time and I've seen many great sprites here.
I want to learn something and improve my skills.

Here are some of my trees for a start:

(free to use)
I am open to criticism and advices: D

Do you have any suggestions what I can try to draw for practise?
Do you need some simple sprites? I can try to draw it in my free time.
PS. at the moment I don't draw outfits, it seems to be too difficult to...

[Keal Atis] Learning to draw sprites