Familiarize the preschooler with numbers 0 through 9. Use a number line or flash cards to show him what each number looks like, and the proper order to list the numbers. Help him make connections with the numbers by making statements like "Zero looks like letter 'O'." Continue to work with him on this, until he can correctly identify each number.
Have the preschooler write out numbers using modeling clay, shaving cream or sand. Some preschoolers are still developing their fine motor skills, and may have difficulty holding a pencil correctly and writing. Show the child he can write numbers in the sand, cream or clay using the tip of his finger. Write one number yourself, using your finger tip, then instruct him to do the same. Praise the child whenever he correctly makes a number, and aid him when he needs your assistance.
Practice number writing on blank paper using crayons or markers. Don't worry if the numbers don't look perfect, or if they are disproportionate, as long as the numbers resemble what they should. Continue to have the preschooler practice making numbers until her skills are advanced enough that you feel she can write them correctly and neatly with pencil.
Instruct the preschooler to write out letters 0 though 9 with a pencil on lined paper. Lined paper gives the child parameters in which to write each number, and helps her make the numbers straight and neat. Have the preschooler write the same number several times, until she can write it correctly and neatly with little or no difficulty.
Provide the preschooler with tips and sayings to help him remember how to write each number. For example, instruct the child to remember how to write an 8 by telling him it looks like a loop de loop, or that a 3 looks similar to a capital letter B. Allowing the child to make different connections with the number shapes helps him better remember how to form each number.