Find out what type of schools are available to your child. This is the most common area where children need someone to advocate for them. Some states have special-needs schools, and others do not. Those states have special classrooms within their school for special-needs kids. Find out which type of school is available to your child, and make an appointment to visit it.
Fill out an IEP (Individualized Education Plan) for your child. No matter which school is available to you, you are required to fill out this paperwork for your child. The IEP is a big pain in the butt, but you will be thankful you have this document, which is considered legal and binding in a court of law. Because of this, you should add as much information to it as possible. If it is not documented in the IEP, your child's school does not have to follow it. Your first year may be trial and error as you learn what needs to be included and what can be taken out.
Make sure you have included everything you possibly can in the IEP. Consider adding the number of therapy sessions you want your child to have per week and which types of therapy, requirements for a 1:1 aide for everyday activities and on the bus and field trips, requirements for special eating arrangements, requirements for an air-conditioned bus and so forth. No matter how silly a thing you think your child needs, add it!
Request a hearing if necessary. If your school is not adhering to the IEP and you have contacted them unsuccessfully, you can request a hearing. Each state has a different address, but you will have all that information given to you when your IEP is created, so make sure you save all the documents. If your issue is not satisfactorily handled at the hearing, you can bring your matter before the judge. The school knows how binding the IEP is, so most of the time you will never have to request a hearing.
Stand your ground when dealing with doctors. If you feel something is wrong with your child and your doctor insists there isn't, you need to take action. Demand to see a specialist (of course, demand it in a nice tone of voice). Almost all doctors will give you a referral to see a specialist. There are pediatricians who specialize in special-needs children, and they will be more open to listening to your complaints and finding whatever is wrong. Don't discount your parental intuition.
Stand your ground when dealing with insurance companies. Along with the doctor, you are going to need to advocate for your child with the insurance companies. They may try to deny anything extra that your child needs. Don't give up. Get documentation from doctors and therapists to back up your claims. Also check with other parents about what your insurance company may cover. In most cases, you can get diapers for free after the age of 3 (we even get Pediasure delivered to our door each month). The insurance companies won't tell you this, but you can find out by asking other parents or your doctor.
Imagine you are the child with the special needs. Advocating for your child can be nerve-racking at times, but it has to be done. Try to imagine that you are the child with the special needs and what would you want someone to do for you. Oftentimes thinking about the situation like that will give you the right perspective and the direction you need to become a very strong and effective advocate for your child.