True. Very good advice. I’ve also been told to skip using the word “the” in all encrypted communications in order to increase the complexity of potential decryption.
Another trick is to include intentional mispellings in the plaintext. The message will still be readable once decrypted, but it even just a few typos sprinkled in will make decryption a bit harder, especially if you do it on words that the decrypter might guess would be related to your subject matter.