Since you are explicitly also asking to handle columns that haven't yet been filled out, and I assume also don't want to mess with them if they have a word instead of a number, you might consider this:
=If(IsNumber(K23), If(K23 > 0, ........., 0), 0)
This just says... If K23 is a number; And if that number is greater than zero; Then do something ......... Otherwise, return zero.
In ........., you might put your division equation there, such as A1/K23
, and you can rest assured that K23 is a number which is greater than zero.