In writing a series of stories about the same characters, plan the whole series in advance in some detail, to avoid contradictions and inconsistencies.

It does not pay a prophet to be too specific.

Speech sounds can be analyzed into fundamental units called phonemes these move around like protozoa in a drop of water, and, like protozoa, join together and split up.

Therefore, no matter how the world makes out in the next few centuries, a large class of readers at least will not be too surprised at anything. They will have been through it all before in fictional form, and will not be too paralyzed with astonishment to try to cope with contingencies as they arise.