Agreed with MasterSky about the dithering. I recommend practicing without dithering to get a feel for how to work with colour, and then using dithering when you really need it. In particular, on the potion itself, almost the entire thing is dithered, there's hardly any space that isn't dithered, giving the potion no colour identity of its own. Personally, I tend to avoid dithering because while it blended nicely on CRT screens, it tends to look very obvious on newer screens, looking too rough for a smooth surface, and too regular for most textured surfaces.
Another thing to consider: the thickness of the glass vessel. Realistically, it could be quite thin, but in artwork that doesn't tend to look as good/natural as glass with exaggerated (read: visible) thickness.
the dithering really doesnt work here.i like the design of the bottle but the dithering makes it look like it has a dull texture and is somewhat rough.
its a good start nonetheless! keep it up 
@MasterSky
Oh whoa. I really see what you mean with the dullness and the texture. I'll think about my material from now on before I use dithering!
Thank you so much for your feedback! I'm a beginner, so I really appreciate it. <3
@eishiya
Thank you so much for your detailed feedback! I'll be following your advice from here on out. I'm very new to pixel art, so I really appreciate it! I come from realistic graphite drawings, so I need all I can get. <3