Well here are some tips I could think of as I paint quite regulary :)
1. It's always easier if on the sketch phase you divide whatever you're painting into planes. Making it a bit more geometrical ends up in easier value estimating. And then in the later process you can smooth some of the edges, and maybe leave some sharper if you're going for a more stylized look (some should ofcourse stay sharp because well, they are sharp irl) I wrote about that because from what I see here, you're mostly working on making things round and smooth and it kinda lacks the three dimensional feel

2. I think you could throw some practical color theory bits in here. It seems like the fox is painted only with browns, while the clothes are only painted with blue (the blue parts ofc). IMO it would work better if i.e you'd paint the bottom part of the neck and head in much cooler shade so that the shirt doesn't look glued on the fox. Also! I recently found out a really useful trick- starting with a colored cell shading. Very loosely mark the shaded areas with some color, layer set on multiply (set the opacity where it looks best), erase softly where it's too strong- that helps in choosing colors for further softer painting, colored shadows make miracles!
And, I think adding details like the colored stripes on the cloth would be easier if they were added in a later stage, when you have the colors and values for the clothes set up- you could paint them then with a lower-opacity brush, or on a overlay layer, so that you wouldn't have to set the values for the stripes all over again. It's really easier that way :)

3. checking how the image looks in greyscale during painting can be veryy helpful in finding out what looks wrong, value-wise

4. I absolutely love how you sketched the background!

Hope something from this helps! Good luck!