1. Don't panic. There is no need and people who panic drown. Stay calm and centered and when "that mom" at the playground tells you that you are screwed because you didn't do this-and-such or didn't get into "the" school. Drop her. She is trouble and she is not correct, and your poor spouse will have to spend a week talking you down, when you should have been laughing with your child.
2. Tour. Even though it is universally known among your neighbors that your zone school is a "disaster" - tour. A lot of this is rumor. Many of these parents that speak with conviction have not toured or attended the schools. You need a baseline. You may find that your school has more things to love than not. Before you go watch this awesome video by InsideSchools.org
3. Support the people that support you. Send a check to your school's PTA AND to InsideSchools.org (the awesome non-profit that will support you in public school for the next dozen years).
4. Don't share your scores. It is bad manners to tell people at the playground what your child got on the ERB or the G&T test, and no one is fooled when you talk about how concerned you are that your child scored so high (don't be worried about telling me, I am a neutral and those scores will come into play with your school choices). You need to remember that other people within earshot may be worried or upset about their child's score and you are only adding to their distress. If someone asks what your child got, say, "Joyce told me not to say."
5. Expect to wait. Then when you get a placement in April or June or July you won't feel like your have been dragged over the coals.
6. If you get a second placement, either in public or private school, release the seat in your previous school. There are anxious parents crying on the wait list. You may have a difficult choice trying to decide between two good options - remember that you are getting good karma, making your decision and quickly passing on a seat to someone who is praying for it.
7. Be positive about getting a good choice that is not your first choice. I have found this to be true in my long and happy life - I have had many expectations about my heart's desire; in my love life, in my college, in my career. What I have found is that often there were benefits available in places that I never expected and that my limited imagination was not nearly as amazing or rich as what life had in store for me. Sometimes when I got my hearts desire I found that it wasn't actually the best thing for me. Embrace the unexpected. Find the good in an unusual situation. A child (or parent) who gets everything they want easily will NEVER be prepared for life - they will lack imagination, grit and tenacity - and they will be boring. This is not to say that there are inappropriate choices. If you don't get an appropriate choice, of course you must advocate for a school that is a better fit. Your child will either see you panicing and crying over missed opportunities or they will see you pick yourself up with grace and hard work to find a suitable placement.