Other, letter based squares usually have some sort of symmetry. Like most of the squares in Abramelin.

What I do, is take names and convert them into numbers using plain Western gematria where A = 1, B = 2 etc.

As an example I made this square of the three superiors of the Grimorium Verum.

Lucifer, Beelzebuth and Astaroth.

I used the spelling as given. This comes to 25 letters with a total numerical value of 111.

111 sadly can not be divided into 5 equal parts, so I made a 5x5 square with 4 columns and rows that add up to 20, and the one central row and column having a value of 31.

This square is then again filled in with the letters by assigning the letters of the first name (Lucifer) to the first number of that value.

From this then sigils can be found. Red for Lucifer, Blue for Beezebuth and Green for Astaroth.

This same square can then also be used to trace sigils for the lesser spirits. For example Clauneck in Purple. This is done on the basis of the numbers (3+3+1+3+5+5+3+2)