They're good, you are improving! If I must critique, then this is what I noticed:

On the first sketch, the outline of the eye is way too dark. Yes, you want the eyes to stand out, but they also have to look part of the face, so shade the eyes more and also shade the area around the eyes. With horses' heads, I often find it useful to try and imagine their skull. If you get a good picture of a horse skull from google, then you'll see all the little convex and concave parts, and these will help you with your shading. Things that are closer to you are darker, things that are further away are lighter.

I I I I I I I I I


Here, for example, stare at the above for a few minutes. You should start to see a sort of passageway, as if you are standing near the dark Is and the furthest point is the lightest I.

I would also say that you are being too neat with your original outlines! I know that's a weird thing to say, but your outline shouldn't be too detailed. Like rutylr mentioned, drawing with circles can help (which is what I do), or simply making a rough outline lightly using your lightest pencil. Your eraser is there for a reason, don't be afraid of using it when your picture starts to take shape to tidy up any loose scribbles.

Your eraser is also good for highlighting light areas, as remember, unless you are in pitch black (which wouldn't make much of a crawing, lol), light has to be falling somewhere. A stroke of the tip of your eraser can bring out this light and make the picture more 3D.

Hope that helps! I have a bunch of sketches I'd like to show you as examples on how to improve yours, but unfortunately SOMETHING *kicks scanner* is stopping me doing so.