Make a schedule and stick to it even if it means putting off house cleaning or errands for a few days. Dedicate time to focus on the child, find things the child enjoys doing and include them in potty training time. Be willing to stretch your boundaries to accommodate for potty training.
Understand there probably will be some potty accidents. Have your child help you clean it up and don't make a big deal out of it and praise your child for their efforts.
As the mom of an Autistic child days can be unpredictable. Keeping a schedule can help make things a little easier while being flexible. If you child loves snacks allow your child to have one while sitting on the potty. If they enjoy watching certain tv shows or movies let them watch one with the potty sitting in front of the tv. If they love video games then let them play them.
You want the child to get the feeling of using the potty. If it works better to go without underwear then do so. While the potty training process may take longer with a special needs child the tools are the same. Be consistent, always praise and utilize things they enjoy.
Also, talk with your child's pediatrician, therapists, even moms of Autistic children or those with special needs. They may have additional ideas to consider. To get started with the basics of potty training consider Pottytrainingsites potty training e-book to help you get started with potty training.