Choose the type of sign language you feel will be most appropriate and beneficial to your child. This decision will be based on factors including his stage of development, his gross and fine motor skills, the area in which you live, and the number and type of people -- carers, teachers, therapists, family members -- who will be using sign language with your child. The sign languages developed and used by deaf people are not universal -- British Sign Language and American Sign Language, for example, are different. Another form of sign language developed specifically for use with individuals who struggle with verbal communication is Makaton. The grammar and motions of Makaton are somewhat simpler than traditional sign languages.
Call a team meeting between all the different people who will be using sign language with your child. Together, and with input from professionals such as sign language instructors or behavioral therapists specializing in autistic spectrum disorders, establish a consistent approach for introducing, mastering and maintaining a sign language vocabulary. Depending on your child's stage of development, you may agree to introduce one new sign word or concept every week, for example. Make sure that everyone who will use sign language with your child is performing the signs correctly and consistently with one another.
Practice each sign with your child in a functional setting. For example, you may introduce the sign for "toilet" or "bathroom" to give your child a way to request a trip to the bathroom. Each time during the day when you take your child to the bathroom, make the sign as you say the word. Your child may mimic you in the sign, or you may need to prompt her using a hand-over-hand technique -- essentially, holding her hands and guiding her to make the sign. As she learns an individual sign, you will not need to prompt so heavily. Any time your child independently makes a learned sign in an appropriate context, provide lots of positive reinforcement to motivate her learning. Examples of positive reinforcement include preferred snacks, hugs and smiles, or anything that your child enjoys.