Good attempts. The lines used here are very fine. I would recommend doing more light sketches so you can prepare yourself for the final lines. And remember, you don't need to draw the whole line in one stroke; you can gradually build it with loose yet calculated strokes.

Your lines are too even in weight and value. Perhaps it is the light you took the pictures in, but try darkening your lines further for the shadows and making your lines thinner for the lights.

These are good sketches. The shapes you used are fairly close; I would have used a rounded triangle for the head. One thing to look out for when drawing the fur is the "saw-blade problem, where your fur looks like the teeth of a saw rather than fur. Try keeping the fur pointing toward the direction it is flowing, as well as varying the sizes of the triangles to avoid symmetry. Nice work so far.

These are great attempts. If you catch yourself erasing a lot, I'd suggest sketching with a lighter pencil first. You can also try Stan's line darkness exercise before you start sketching. Great work with these sketches, you're on the right track.