Have a good idea of the probability of what you want even being available at seven months. And then have multiple choices for your switch. For instance, if you want BCV in the Summer, you'll need luck, but if you are willing to take BCV/BWV (any View), then VGF, Poly, Riv, etc, you can go down the list until you switch.
Or you can book what you can, waitlist, and try to piece something together. That's too much stress for me, so I've always switched at seven months with a list. But then we also bought where we don't mind ending up, so we are happy if we end up with the reservation we made at home.