My first piece of advice is to listen to what your principal and other staff are saying and what they're not saying. There are some rare schools where they really don't have any intention of helping your child. Maybe they want to keep grade-point averages up or maybe there's prejudice and misunderstandings, the reason doesn't really matter. You want to identify them as quickly as possible and then not waste any time with them. If they keep bringing up new hurdles for you to jump over, then they're not trying to work with you, they're trying to say "no" without actually saying "no". If they refuse to let you look at the school or any "special arrangements" they've made for your child, be very suspicious. Sometimes the "autism room" is a repurposed broom closet or a corner in a busy classroom or a corner of the principal's office. If they're claiming they have a space set up, you have the right to look at it before your child comes to school.
My second piece of advice is not to come in with a chip on your shoulder about the education system. It's difficult, given how vigilant special needs parents need to be, but it's too easy to get trapped in a cycle of hostility. My personal tactic is to play stupid and insist on everything being spelled out to me in great detail. That gives me a good understanding of how willing the staff are to be helpful, it gives me an opportunity to start figuring out any holes in their plan. Always try to remember that while people may not always have the information to get things right, the majority do want to help.
My third piece of advice is to play the bureaucracy game with them. Insist on getting everything in writing. I insist on email communication or summations of any plans and when we have in-person meetings, I take notes. At the end of the meeting, I jot down a brief summary and have every person in the meeting initial it, agreeing on the actions to be taken. We used to record meetings, but we found it a challenge to go back and get the relevant information we were looking for. I have a notebook that I bring to every meeting, so I have a record of what has been tried, what has been agreed to and what problems have been brought to my attention.
My final piece of advice is to accept the inherent lack of control. If the school is bringing in outside help (speech therapists, occupational therapists, etc), those people are working for the school board. They should send you update and reports but there isn't going to be the kind of detail or frequency we're used to from private services. I get two reports per year with Alex, both less than a page. One is what they intend to do at the start of the year and one is an end of year progress report on those goals. Other than that, I rarely hear from the consultants, but I do get regular updates from Alex's teacher, in part because we are on good terms and she knows I will participate to support their work at home. A good relationship with the staff on the ground, ie, the teachers or EAs, is your best weapon at making sure your child gets what he or she needs.