Make varying strokes
Strokes that are similar in length, width, and distance apart can become boring. Vary them, creating texture, which is visually pleasing.

Let the paper show
Don't be afraid to let the paper show between your pencil marks. In the light areas leave these spaces as they happened. In the shadows let them show, but carefully darken over them. Let pure white paper be the lightest highlight.

Follow the contour
Let the pencil strokes conform to the surface of the horse. As the strokes curve and bend around the horse's shape they will help to visually create the form. Use straight strokes for the flat areas.

Dark accents
These can really make a drawing, but keep them to a minimum. Too many darks can cause your drawing to look over-worked.

Capture the large shapes
Avoid over doing the small shapes. Trying to show a lot of smaller shapes and details will sometimes distort the large shapes, destroying the horse's overall image.

Eraser and shield
Highlights and mid-tones can be achieved by carefully lifting off areas of dark pencil. Dab and lift with the eraser instead of rubbing, so your drawing isn't smeared. Knead your eraser and keep it clean.

Protector sheet
Place a clean sheet of typing paper under your drawing hand. Fold up one corner of the sheet so it can be lifted and moved. Don't slide the paper around on your drawing.