Also, discourage holding the pencil too tightly. It might be a good idea to start your child with a thicker pencil, or place a soft pencil grip on a standard pencil, as larger things are easier for little fingers to hold and manipulate. The slant of the paper is important in teaching your child to write correctly. Your child's paper should be slanted slightly to the right, so that the bottom-right corner is pointing at his tummy. Discourage him from turning the paper completely on its side.
Kindergarten writing paper with one inch writing lines is best for beginners.
Letter formation is very important. It's much better to teach him how to form the letters correctly the first time than to correct an improper formation. Since you have older children, you are probably familiar with the handwriting system used by the school district. Follow that pattern for consistency. In teaching him to write his name, start with tracing.