There are many ways to make Nomenclators better. One of them is to introduce a concept called nulls.

In Cryptography nulls are random characters that mean absolutely nothing. When decrypting a ciphertext if you encounter a null, you should just skip to the next letter.
Nulls are used to alter the frequency analysis and make cryptanalysis harder.

Let us say that this was my key:

ABCDEFGHIJKLMNOPQRSTUVWXYZ
PLOKMIJNUHBYGVTFCRDXESZWAQ

Normally we would encrypt "WELCOME TO EARTH" as
"ZMYOTGM XT MPRXN".

But let's say that we wanted to use nulls to make our cipher better. "ZMYOTGM XT MPRXN" might become "ZM*YOTG*M *XT MPRX*N".

When decrypting we should just skip over the nulls to get "WELCOME TO EARTH".

To make it even harder to preform cryptanalysis we can remove all the spaces. "WELCOME TO EARTH" would become "ZMYOTGM XT MPRXN" would become "ZMYOTGMXTMPRXN". Trying to cryptanalyze a ciphertext without spaces is very challenging.

There are more things you can do. Instead of writing 'XN' to encrypt 'TH'. Create a special symbol for the digraph 'TH'. You can also do the same thing for other common digraphs like 'SH', 'CH', 'ED', and 'CK'. You can also have symbols for other groups of letters like 'ing'.

You can even get really creative and have a symbol that represents deleting the next letter or a symbol that says to ignore the previous letter.