[SamReidHughes]

I try to pick words with different lengths. They're more visually distinguishable.

[jacquesm]

And try to pick words that are lexicographically distant from each other to minimize the chance of single letter typos changing the meaning of the code.

[JadeNB]

Of course it's a tiny matter of terminology, but you probably mean Hamming distant, not lexicographically distant. `zaaaaa` is lexicographically farther from `aaaaaa` than is `bbbbbb`, but Hamming closer.