I made a sloppy edit of the bunny to try to point out a couple of the major flaws in your pieces in general. I was not sure if it was red or pink (it's red right?) so I shaded it in both.
While on the subject of colors, yours need more contrast, at the size you're working on, differences you can see when zoomed in super far to sprite are often indistinguishable when viewed at actual size, so you should usually make sure there is a large amount of contrast between shades. Additionally, instead of simply choosing lighter and darker shades of exactly the same hue, which can make an image look dull, it is often a good idea to shift colors slightly as well, from red to orange or purple, or from pink to purple or red, this is called hueshifting.
Another issue that recurs in many of your pieces is overdetailing, you're trying to cram too much into a very small space, and it ends up looking very messy and is difficult to read, you have to simplify things when working at such a small size. On your bunny, I used more solid chunks of color to help produce a clearer image. Due to the cluttered pixels, I was unable to even tell where your outlines or lightsources were, it looked to me like you were just outlining the left side of the sprite, with the apparent exception of the legs, so I assumed the light was shining from our right. I also neglected to outline the leg for consistency.
You have a good start, I can tell from your sprites that you at least have a brain in your head and some knowledge of how to do things, you just have to remember that what you see as you're drawing and what the piece actually looks like are two different things entirely, and zoom out frequently to check, and also heed the critique/advice that people on this site (like me!) give you.
Oh and in case you didnt know, you dont get to use my edit, that was something I was unaware of when I started spriting
but you can certainly take inspiration from it, that's the whole point of the thing.