Hi, this is my first time posting here. I'm relatively new to pixel art and I was wondering if I could get some feedback on the following cat portrait I've been working on? Thanks! 

Please post your reference if you're using one.
You usually don't even need outlines on an image this size.
Avoid double-outlining things like you've done with the blue in the eyes, it doesn't do you any favours.
Pillow-shading is bad and you've got it all around the edges of the ears and kind of happening on the nose and brow.
Remove very similar colours.
I suggest a paint over on another layer if your software supports it.
Here's a workflow you can't go wrong with:
First establish a light source or 2 and try to block in your basic forms, you can even use pure greys at this point just to get values.
As mentioned by others, work rough and painterly and don't get into detail.
You only need about 3 shades at this point.
Now block in basic details like the eyes, still using grey to just get the values.
Once you clean it up a bit and are happy with the shapes you can start to blend in some saturation (use a colour picker HSB mode).
Then you'll need to tweak colours again as adding saturation usually affects the perceived value.
Around this point is a good time to start adding details like fur texture.
I suggest spending some time studying pixel texturing techniques.
What you'll see is its easier to create texture along the edges between light and dark.
So you can experiment with stuff like grass around the edges of a tree's shadow.
Same technique can be applied to many textures such as fur.
Texturing example (don't freak out! just look at the grass

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