I draw most of the lines vertically to achieve a nice even color; however, there are instances where the lines need to be drawn in the direction following the flow of the object you are drawing. Hair is a good example of this. Another example is in the case of grass and trees, the lines for branches and twigs are drawn in the direction they are growing.
A sharp pencil allows the lead to fill in the small bumps and indentations of the textured paper to create an even color. If the pencil is dull, the lead will skip the indentations and create white holes throughout the area. The pencil can be rotated in your hand, in order to help keep the point sharp longer.
For any specific area scheduled to receive a blending of colors, always start with the lightest color first, then slowly build up with gradually darker colors to achieve the desired effect.
A last piece of advice I can give, which is one of the easiest things to do, but also one of the most important: Prior to beginning your drawing, always carefully inspect the paper in order to insure it is in perfect shape. Obviously, you can easily see if it's clean, but you also need to make sure there are no scratches or indentations in it. (I learned this the hard way!) Hold the paper up and view it at an angle in a brightly lighted room. Check to make sure that the entire surface is a smooth, uniform, consistent texture. If there are any scratches or dents, the pencils will not fill in those areas uniformly, and your finished drawing will contain white marks and/or blotches.