The key is to understand which way return current of each signal is going back to the source. To have lot of GND planes may be not enough. If signal track jumps from being over one zone to be over second zone the return current has a problem and when it travels long way depending on circuit it can emit noise or be sensitive to interference.
If you want to learn PCB design my suggestion was to read:
and:
and it (my suggestion) didn’t changed since that time.
My solution for 2 layers is to always have continuous GND plane at one layer. An example of such PCB I shown here: